First Alert CO250 Tamper-Resistant Battery CO Alarm Review (4.2/5) | WC Safety
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.
Related: CO Detector Placement Guide 2026 | First Alert CO400 Review | First Alert CO600 Review | Best Smoke Detectors 2026
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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.
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.