First Alert
First Alert SC9120B Hardwired Combination Smoke & Carbon Monoxide Alarm with Battery Backup
$53.98
Reference price as of 2026-08-23 — check Amazon for the current price and stock.
Right for homeowners replacing an existing hardwired First Alert/BRK smoke+CO circuit who need a matching drop-in unit; new installs should consider the current SMICO100-AC replacement instead.
Full spec sheet
| Key specs | |
| Brand | First Alert |
| Price | $53.98 |
| Capacity | — |
| Continuous output | — |
| Peak / surge output | — |
| Weight | 0.7 lb |
| Battery chemistry | — |
| Dimensions (L x W x H) | 5.6 x 5.6 x 1.9 |
| Includes solar panel | No |
| Use cases | Home, Apartment |
| Other verified specs | |
| Type | Combination smoke (ionization) + CO (electrochemical) |
| Detector power source | Hardwired 120V AC with 9V battery backup |
| Status | Discontinued by manufacturer, superseded by SMICO100-AC — price is a third-party retailer estimate, not manufacturer-confirmed |
Pros
- Combines ionization smoke and electrochemical CO sensing in one hardwired unit, covering two hazards with one install
- 9V battery backup keeps it working through power outages, exactly when fire/CO risk from candles or generators rises
- Interconnects with other compatible First Alert/BRK hardwired alarms so one trigger sounds the whole house
- Latching alarm indicator shows which sensor tripped even after the alarm clears
Cons
- Discontinued by the manufacturer and replaced by the SMICO100-AC — future replacement units may be harder to source
- Hardwired install requires an electrician or existing alarm wiring, unlike battery-only alarms
- Uses older ionization smoke sensing, which reacts more slowly to smoldering fires than photoelectric sensors
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