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Industrial Safety Equipment, PPE Guides & Reviews
Industrial Safety Equipment, PPE Guides & Reviews
BRK 9120B Hardwired Ionization Smoke Alarm, Interconnectable with Battery Backup product photo
May 14, 2026 Steven Eaton

Co250 First Alert Tamper Resistant Battery Co Alarm Review

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.

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

Published · Last updated

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: 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.

Related: CO Detector Placement Guide 2026 | First Alert CO400 Review | First Alert CO600 Review | Best Smoke Detectors 2026

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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

Common questions

Sources. Requirements referenced here come from OSHA 29 CFR 1910 and the NIOSH recommendations. Where a consensus standard governs, the ANSI document is named in the text.

Related reference

Neighbouring references on this site: 10 year sealed vs replaceable battery smoke alarms, best first alert smoke detector 2026, and kidde vs first alert co alarms.

Why trust WC Safety

WC Safety is an independent, affiliate-supported review site. It is not a retailer: it holds no inventory, takes no orders, and earns only from qualifying purchases through clearly marked links — which never changes what a product is rated to do. Standards language is taken from the regulation text directly, and ratings are reported as the manufacturer publishes them. We run no laboratory and perform no testing of our own. Where published sources disagree, we say so and plan on the conservative figure rather than the flattering one.

Our methodology

Figures come from the regulation and the published specification, in that order. Derated numbers are calculated, not estimated. Nothing here is presented as a measured result, because we measure nothing.

Researched and written by Steven Eaton, editor of WC Safety. Steven holds no safety certification and does not test products; this page compares what manufacturers and regulators publish, with the gaps in that record marked. Last reviewed August 2026.

Affiliate disclosure: as an Amazon Associate, WC Safety earns from qualifying purchases. WC Safety is not a retailer and takes no orders — links go to the seller, and the price you pay is unchanged.

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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