May 14, 2026 Updated July 9, 2026 Steven Eaton

First Alert CO250 Tamper-Resistant Battery CO Alarm Review (4.2/5) | WC Safety

WC Safety Editorial Verdict: 4.2/5

WC Safety Editorial Verdict: 4.2 / 5. The First Alert CO250 is a single-purpose tool done well: a UL 2034 battery CO alarm whose tamper-resistant locking cover defeats the single biggest cause of dead alarms in rentals and dorms — occupants pulling the 9V battery. We score it editorially (we have no verified customer rating for this unit), and the deductions are honest trade-offs rather than flaws: no digital ppm display, no interconnect, and a replaceable battery that demands an annual maintenance touch rather than the set-and-forget convenience of a sealed 10-year alarm. For owner-occupied homes a sealed 10-year alarm with a display is the smarter buy, but for anyone managing CO compliance across units they don't occupy, the CO250 is the correct pick — compare the field in our best carbon monoxide detector 2026 guide.

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First Alert CO250 Review: Tamper-Resistant CO Alarm Built for Property Managers and Rental Units

Battery removal is the leading cause of non-functioning CO alarms in rental properties and institutional settings. A tenant who finds the CO alarm's chirp annoying — or simply wants to borrow the battery for another device — can disable critical life-safety equipment in seconds. The First Alert CO250 is designed specifically to prevent this: its tamper-resistant locking cover requires a key or tool to open, making unauthorized battery removal significantly more difficult and deterring casual disabling.

This is not a feature most homeowners need. But for landlords, property managers, dormitory administrators, and facilities personnel responsible for CO compliance across units they do not occupy, the CO250 solves a problem that has resulted in preventable deaths. This review covers whether it solves that problem effectively and where it sits among First Alert's full CO alarm lineup.

Quick Verdict: 4.2 out of 5. The CO250 earns its premium over the CO400 for any property manager who has dealt with disabled alarms or regulatory citations. The tamper-resistant design is well-executed, the 7-year warranty is solid, and UL 2034 certification meets all residential code requirements. The limitation is the same as all battery-only alarms: no display, no interconnect, no ppm readout.

CO250 Specifications

Feature	Detail
Model Number	CO250 / CO250B
Power Source	9V battery (included)
Sensor Type	Electrochemical
Alarm Output	85 dB at 10 feet
Certification	UL 2034 Listed
Tamper-Resistant Cover	Yes — locking cover, key/tool required
Digital Display	None
Interconnect	No
End-of-Life Warning	Yes
Warranty	7 years
Mounting	Wall mount

The Battery Removal Problem: Why It Matters

Research into CO alarm non-function consistently identifies missing or dead batteries as the primary cause. NFPA data shows that in homes with CO alarms that failed to operate, battery problems — including deliberate removal — account for a large share of failures. In multi-tenant settings, this is amplified: occupants who disable an alarm for any reason leave the unit silent for subsequent occupants who may never check it.

Standard CO alarms, including the First Alert CO400, can have the battery removed in about 10 seconds. The CO250's locking cover adds a meaningful deterrent — it requires a flat-head screwdriver (or the included key tool, depending on variant) to open the battery compartment. This does not make it tamper-proof in an absolute sense, but it prevents the casual removal that accounts for most incidents. An occupant who genuinely wants to disable the alarm has other means — but most disabling events are impulsive, not deliberate, and a simple mechanical barrier stops most of them.

How the Tamper-Resistant Cover Works

The CO250's cover is secured by a locking mechanism — typically a screw or slide lock — that requires a screwdriver or the included tool to release. The cover cannot be removed by hand under normal force. This design is used in similar tamper-resistant fire alarm products (CO250 mirrors Kidde's tamper-resistant alarm design philosophy) and has been proven effective in institutional deployments.

Importantly, authorized personnel — property managers, maintenance staff — can still change the battery when needed. The tamper resistance is a deterrent to unauthorized access, not a permanent seal. Battery replacement on a maintenance schedule (annually) remains fully practical. First Alert recommends documenting CO alarm battery replacement dates as part of a property maintenance log — the CO250's design supports this systematic approach.

Regulatory Context for Rental Properties

As of 2026, the majority of U.S. states require landlords to install and maintain working CO alarms in rental units with fuel-burning appliances or attached garages. State laws vary in their specifications — some require only UL 2034 certification, others specify battery backup or interconnect capability. None specifically require tamper-resistant designs, but tamper resistance is the mechanism by which landlords can demonstrate ongoing compliance between tenant changeovers.

Under most state tenant-landlord laws, the landlord is responsible for ensuring the CO alarm is functional at move-in and the tenant is responsible for not tampering with it. The CO250's design provides physical evidence of the landlord's compliance intent — and practically ensures the alarm remains operational regardless of tenant behavior.

For workplace CO monitoring under OSHA 29 CFR 1910.1000, see WC Safety's industrial respirator collection, which includes half-face respirators and full-face respirators equipped with CO/organic vapor cartridges for high-exposure environments.

Performance: UL 2034 Compliance and Sensor Quality

The CO250 uses the same electrochemical sensor platform as First Alert's other residential CO alarms. It meets all UL 2034 response time thresholds:

70 ppm: Alarms within 60–240 minutes
150 ppm: Alarms within 10–50 minutes
400 ppm: Alarms within 4–15 minutes

The 85 dB alarm output at 10 feet is consistent with the CO400 and CO600 — loud enough to wake sleeping occupants through closed interior doors under normal conditions. The 7-year warranty reflects the expected service life of the electrochemical sensor. After 7 years, the entire unit should be replaced rather than reused — sensor drift after this period can cause the alarm to fall outside UL 2034 thresholds.

CO250 vs. CO400 vs. CO710: Which First Alert CO Alarm Is Right for You?

Feature	CO400	CO250	CO710
Power	9V Battery	9V Battery	AC + 9V Battery
Tamper-Resistant	No	Yes	No
Digital Display	No	No	Yes (ppm)
Interconnect	No	No	Yes
Warranty	5 yr	7 yr	7 yr
Best For	Budget/supplemental	Rental/institutional	Primary residential
Price Range	Budget	Mid	Mid-High

Pros

Tamper-resistant locking cover — solves the #1 cause of alarm non-function in rentals
UL 2034 certified — meets all residential and commercial code requirements
7-year warranty — longer than the CO400, same as CO710
Electrochemical sensor — accurate, selective CO detection
Battery-powered — no wiring, works during power outages
85 dB alarm output
End-of-life warning included

Cons

No digital ppm display
No interconnect — cannot link to alarm system
Tamper resistance is a deterrent, not absolute prevention
Slightly more expensive than CO400 for the same detection capability
Not necessary for owner-occupied homes

Who Should Buy the First Alert CO250

Landlords and property managers responsible for CO compliance in tenant-occupied units
Dormitory and student housing administrators where battery removal is a chronic problem
Hotel and short-term rental operators needing reliable CO protection across guest rooms
Commercial facility managers in settings where maintenance staff are the only authorized personnel to access alarm batteries
Group homes, assisted living facilities, and similar institutional settings

Who Should Choose Something Else

Owner-occupied homes — the tamper resistance adds cost without meaningful benefit when the homeowner controls all access
Homeowners wanting a display — the CO710 adds digital ppm readout and interconnect for primary whole-home coverage
Smart home users — First Alert's OneLink series or the Nest Protect provide app integration that the CO250 does not

For complete placement guidance on CO alarms — how many you need, exactly where to put them, and which models suit each location — see our CO Detector Placement Guide 2026. For integrating CO detection with smoke alarm coverage, see our Best Smoke Detectors 2026 guide covering combination alarms and whole-home systems.

Check current pricing for the First Alert CO250 on Amazon Check Price on Amazon →

Frequently Asked Questions — First Alert CO250

Q: How does the tamper-resistant cover on the CO250 work?

A: The battery compartment cover is secured by a mechanical lock — a screw or sliding latch that requires a flat-head screwdriver or the included tool to open. It cannot be removed by hand under normal force, preventing casual or impulsive battery removal by occupants.

Q: Can I still change the battery if I'm the property manager?

A: Yes. The locking mechanism is accessible to authorized personnel with the correct tool. First Alert recommends annual battery replacement — the CO250 fully supports planned maintenance schedules, just not unauthorized access by occupants.

Q: Is the CO250 required by law for rental properties?

A: No law specifically requires tamper-resistant CO alarms as of 2026. Most state laws require UL 2034 certified alarms in rental units — the CO250 meets this. The tamper-resistant design is a best practice that protects landlords from liability and ensures continuous compliance.

Q: What is the difference between the CO250 and CO250B?

A: CO250B is a variant SKU — typically identical in specifications, with the suffix indicating a retailer-specific or bundle variant. Both carry UL 2034 certification and the same tamper-resistant cover design.

Q: Does the CO250 have a digital display showing CO ppm levels?

A: No. The CO250 alarms at dangerous CO thresholds but does not display real-time ppm readings. For a digital display, choose the CO710 or a combination unit with a digital readout.

Q: Can a determined tenant still disable the CO250?

A: A genuinely determined individual with tools could eventually access the battery compartment. The tamper-resistant design prevents casual, impulsive, or accidental disabling — which accounts for the vast majority of incidents. It is a strong deterrent, not an absolute barrier.

Q: How long does the battery last in the CO250?

A: Approximately 1 year under normal operation. First Alert recommends annual battery replacement. The low-battery chirp activates when battery life is critically low — but for rental properties, proactive annual replacement on a maintenance schedule is preferable to waiting for the chirp signal.

Q: Is the CO250 UL 2034 certified?

A: Yes. The CO250 carries full UL 2034 listing, meeting all response time requirements at the 70 ppm, 150 ppm, and 400 ppm CO concentration thresholds required by the standard.

Q: What is the CO250's warranty?

A: The CO250 carries a 7-year warranty from First Alert — two years longer than the entry-level CO400, and matching the CO710 and CO600.

Q: Can the CO250 be connected to a home security system?

A: No. The CO250 does not have interconnect capability. For integration with hardwired alarm systems, choose a First Alert model with interconnect (such as the CO710) or a professionally monitored CO detector.

Q: Does the CO250 detect smoke?

A: No. The CO250 is a dedicated CO alarm only. For combination CO and smoke detection in rental units, see First Alert's SCO series combination alarms.

Q: Where should I place the CO250 in a rental unit?

A: Follow NFPA guidance: one CO alarm on every level of the dwelling, and one outside each sleeping area. Mount the CO250 on the wall at the recommended location — its wall-mount design is specifically suited to fixed installation where the property manager controls placement and access.

Q: How does the CO250 compare to the CO400 for rental use?

A: For rental properties, the CO250 is the clear choice. The CO400 is a better value for owner-occupied or supplemental use, but its open battery compartment makes it unsuitable in settings where tenants might remove the battery. The CO250's tamper resistance addresses this directly and the 7-year warranty (vs. CO400's 5-year) further justifies the modest price premium.

Q: Can I use the CO250 in a hotel or Airbnb?

A: Yes — the CO250 is well-suited for short-term rental settings (hotels, Airbnb, VRBO) where guests change frequently and property access between stays may be limited. The tamper-resistant cover ensures the alarm remains operational throughout multiple guest stays.

Q: What happens when the CO250 reaches end-of-life?

A: The CO250 emits an end-of-life chirp signal distinct from the low-battery chirp when the electrochemical sensor reaches the end of its 7-year rated service life. Replace the entire unit at this point — do not simply replace the battery. The property manager should document replacement in the maintenance log as evidence of compliance.

Q: Is the CO250 available in multi-packs for property managers?

A: Yes. The CO250 is typically available in multi-unit packs from major distributors, making it practical for landlords outfitting multiple units simultaneously. Check availability at Check Price on Amazon → for current multi-pack pricing.

Final Verdict

Rating: 4.2 / 5.0

The First Alert CO250 earns a 4.2 because it solves a real, documented problem with a practical, well-executed solution. Battery removal is the leading cause of CO alarm non-function in rental and institutional settings — and the CO250's tamper-resistant cover directly addresses this. For property managers, dormitory administrators, and anyone responsible for CO compliance in spaces they do not personally occupy, the CO250 is the correct choice over the CO400. The absence of a digital display and interconnect capability are limitations, but not failures — they are appropriate trade-offs for a unit whose primary purpose is reliable, persistent operation in managed multi-unit environments.

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Disclosures & editorial standards
WC Safety participates in the Amazon Services LLC Associates Program. Outbound Amazon links are affiliate links. We accept no manufacturer payment, sponsorship, or product samples. This content is not medical, legal, or regulatory advice. Safety equipment selection is governed by applicable OSHA standards and your facility's safety program.

Pros & Cons

Pros

Tamper-resistant locking cover requires a tool to open the battery door, blocking the impulsive 9V removal that disables most CO alarms in rentals and dorms
UL 2034 listed and meets every residential and commercial code response threshold (70 ppm / 150 ppm / 400 ppm)
7-year warranty matches First Alert's premium CO710/CO600 and beats the entry-level CO400's 5-year coverage
Battery-only operation keeps detecting through power outages with no wiring or outlet required
85 dB alarm is loud enough to wake sleeping occupants through a closed interior door
Wall-mount, fixed-install form factor suits property managers who want to control placement and access

Cons

No digital display, so it never shows real-time CO ppm levels the way the CO710 or a low-level monitor does
No interconnect, so it cannot link to other alarms or a building fire/security system
Replaceable 9V battery needs annual swaps and adds a recurring maintenance task versus a sealed 10-year unit
Tamper resistance is a deterrent, not absolute prevention — a determined occupant with tools can still reach the battery
Overkill for owner-occupied homes, where the locking cover adds cost without real benefit

Who It's For

Buy it if:

Landlords and property managers responsible for CO compliance in tenant-occupied units who keep getting alarms with the battery pulled
Dormitory, student-housing, and group-home administrators where casual battery removal is chronic
Hotel, Airbnb, and short-term rental operators needing alarms that survive frequent guest turnover
Commercial and institutional facility managers where only maintenance staff should touch alarm batteries
Buyers who specifically want a battery-only CO alarm (no wiring, works in outages) plus anti-tamper protection

Look elsewhere if:

Owner-occupied homeowners, who control all access and gain nothing from the locking cover — a standard plug-in or sealed alarm is cheaper
Anyone who wants a digital ppm readout, interconnect, or whole-home linking (look at the CO710 or a hardwired interconnect model)
Buyers who prefer never touching a battery for a decade and should choose a sealed 10-year alarm
Sensitive occupants wanting earlier warning, who need a low-level CO monitor rather than a standard UL 2034 alarm

Related Resources

Frequently Asked Questions

Is a replaceable-battery CO alarm like the CO250 better or worse than a sealed 10-year unit?

It depends on who controls the alarm. The CO250's replaceable 9V battery is an advantage in managed rentals because staff can verify and swap batteries on a documented schedule, and the tamper cover stops occupants from removing them. For an owner-occupied home, a sealed 10-year alarm like the CO710 or Kidde's C3010D is more convenient because there is no annual battery task — you replace the whole unit at end of life.

Should I choose the CO250 or a plug-in CO alarm with battery backup?

Choose the CO250 when you need a battery-only alarm that keeps working through outages and you want anti-tamper protection in a unit you don't occupy. Choose a plug-in alarm such as the First Alert CO600 or Kidde's plug-in with battery backup when an outlet is available and you prefer continuous AC power with the battery only as a fallback. Plug-ins are convenient for homeowners; the CO250 is built for tenant-occupied compliance.

Does the CO250's standard UL 2034 alarm protect sensitive people as well as a low-level monitor?

No. The CO250 trips at standard UL 2034 thresholds (roughly 70 ppm sustained over 1-4 hours, faster at higher concentrations), which protects healthy adults but tolerates lower CO that can affect infants, pregnant occupants, the elderly, or people with heart or lung conditions. Those households benefit from a low-level CO monitor such as Kidde's low-level alarm or the 10-year low-level model, which warn earlier than the UL 2034 minimum.

Is the interconnect capability the CO250 lacks worth paying for?

Interconnect matters most in larger or multi-level homes where one alarm sounding all units gives occupants more escape time. The CO250 cannot interconnect, so if you want every alarm to sound together you need a wired model like the Kidde hardwired interconnect CO alarm. For a single rental room or a small unit where one audible alarm covers the sleeping area, the CO250's lack of interconnect is not a real loss.

How many CO250 alarms do I need and where should they go in a rental unit?

Place one CO alarm on every level of the dwelling and one outside each separate sleeping area, per NFPA guidance. CO mixes evenly with air, so mounting height is flexible — follow the unit's manual. Our co detector placement guide 2026 walks through exact counts and locations for multi-bedroom and multi-story layouts so you don't under-cover a unit.

Why does the CO250 score 4.2 instead of higher?

It executes its narrow job — tamper-resistant battery CO detection — very well, which earns a strong score. It loses points only for what it intentionally omits versus premium alarms: no digital ppm display, no interconnect, and a replaceable battery that needs annual attention. Those are appropriate trade-offs for a compliance-focused rental alarm, not defects, so it lands at 4.2 rather than near the top of the best carbon monoxide detector 2026 field.

Do I still need a smoke alarm if I install the CO250?

Yes. The CO250 detects only carbon monoxide, not smoke or fire. Every dwelling needs both, either as separate alarms or as a combination smoke/CO unit. Pair the CO250 with a dedicated smoke alarm from our smoke detectors collection, and see the best smoke detectors 2026 guide for combination and whole-home options.

Is the CO250 better than buying a combination smoke and CO alarm for a rental?

A combination unit covers both hazards in one device and is convenient, but it ties the smoke and CO sensors to a single replacement clock and rarely includes tamper-resistant battery locking. The CO250 is the better pick when the specific problem is occupants pulling CO alarm batteries; run it alongside a separate smoke alarm. If anti-tamper isn't a concern, a combo unit from the smoke detectors range can simplify installation.

When do I replace the CO250 itself, not just its battery?

Replace the entire CO250 at the end of its 7-year rated service life, signaled by a distinct end-of-life chirp, because the electrochemical sensor drifts and can fall outside UL 2034 limits after that point. The battery is a separate annual task. For how to confirm an alarm is still responding between replacements, see how to test a smoke and co alarm.

How does the CO250 compare to the First Alert CO710 for whole-home coverage?

The CO710 is the better primary residential alarm: sealed 10-year battery, digital ppm display, and a 7-year warranty with no annual battery swaps. The CO250 wins only on tamper resistance for units you don't occupy. For your own home, choose the CO710; for tenant units, choose the CO250.

Is the CO250 a good value compared with the cheaper CO400?

For owner-occupied or supplemental use, the CO400 is the better value because it offers the same detection at a lower price. The CO250's premium is justified only when tamper resistance is needed — the locking cover plus the longer 7-year warranty (versus the CO400's 5-year) pays off in rentals and institutions where disabled alarms create liability and risk.

Does a digital display add enough value to skip the CO250 for a homeowner?

For many homeowners, yes. A display showing real-time ppm helps you spot low-level CO trends and confirm a reading during an alarm event, which the CO250 cannot do. If that matters to you, look at the CO615 plug-in with display or a Kidde battery CO alarm with digital display. The CO250 deliberately omits the display to stay simple and fixed-install for managed units.

Will the CO250 work where there is no power outlet?

Yes. The CO250 runs entirely on its 9V battery, so it installs anywhere on a wall without an outlet or wiring and keeps detecting during power outages. That makes it suitable for interior hallways, older units, and locations where running AC power is impractical. Browse the full battery and plug-in range in our carbon monoxide alarms detectors collection.

How do I choose between First Alert and Kidde for a tamper-resistant rental alarm?

Both brands make code-compliant UL 2034 alarms; the deciding factors are tamper design, battery format, and warranty. The CO250 leads on its locking battery cover. If you also want a long sealed life in a managed setting, compare Kidde's 10-year battery alarm and the worry-free 10-year sealed models, which remove the annual battery task but lack the CO250's keyed cover. Match the alarm to whether your priority is anti-tamper access or set-and-forget sealed life.

Can I mix the CO250 with other CO and smoke alarms across a property?

Yes. Because the CO250 is a standalone (non-interconnected) alarm, you can deploy it unit-by-unit and combine it with plug-in, hardwired, or sealed alarms elsewhere on the property as each location demands. Just keep each unit on its own replacement schedule. Shop compatible models across the co detectors range to standardize your maintenance program.

Why trust WC Safety
Industrial PPE specialists. We do not accept manufacturer payment for placement.

Reviewed by
Steven Eaton, WC Safety Editorial Team — guidance reflects current OSHA, NIOSH and ANSI practice.

Our standards
Ratings combine published specs, hands-on familiarity, and verified customer data where available; we do not fabricate lab tests.

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Filed in: battery-co-alarm, co-alarm-review, CO250, first-alert, product-review, property-management, rental-co-alarm, tamper-resistant-co-alarm, UL-2034

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