Smoke Alarms vs. Combination Smoke/CO Alarms

When you're managing a multifamily property, safety and compliance are always top priorities. One common question property owners face is whether to install combination smoke and carbon monoxide (CO) alarms or to keep separate devices for each hazard. Both approaches can meet code, but the right choice for your property depends on regulations, building layout, and long-term maintenance considerations. 

Why It Matters 

Smoke and carbon monoxide are two of the most serious life-safety risks in residential buildings. 

• Smoke alarms detect early signs of fire through photoelectric or ionization sensors. 
• CO alarms detect carbon monoxide—an invisible, odorless, and colorless gas created when fuels burn incompletely from sources like furnaces, water heaters, fireplaces, and attached garages. 

In multifamily housing, ensuring reliable coverage for both hazards is not only a compliance issue but also a key part of protecting tenants and reducing liability. 

Combination Smoke/CO Alarms 

Pros: 

• A single device covers both hazards, reducing clutter on walls and ceilings. 
• Simplified installation and maintenance with fewer units to test. 
• Cost-effective for initial installation. 
• Many jurisdictions allow or encourage their use in multifamily housing. 
• Streamlined tenant education on testing procedures. 

Cons: 

• If the unit fails, both smoke and CO protection are lost simultaneously. 
• Replacement can be more costly since both functions are tied to one device. 
• May have limitations in optimal placement (smoke detection works best on ceilings, while CO detection can be effective at multiple heights). 
• Potential for more nuisance alarms if not properly calibrated for the environment. 

Separate Smoke and CO Alarms 

Pros: 

• Dedicated sensors for each hazard, often providing more specialized and sensitive detection. 
• Flexibility in placement—smoke alarms in bedrooms and hallways, CO alarms near fuel-burning appliances and sleeping areas. 
• If one unit fails, the other still provides protection. 
• Can optimize sensor technology for each specific hazard. 
• Easier to troubleshoot issues with individual devices. 

Cons: 

• More devices to install and maintain across multiple units. 
• Testing and tenant education may require more effort. 
• Higher initial installation costs due to more devices. 
• More wall/ceiling space required. 

What the Codes Say 

NFPA (National Fire Protection Association) allows either separate or combination units as long as they are properly listed and certified for both hazards under applicable standards. 

International Residential Code (IRC) governs most multifamily residential units and requires: 

• Smoke alarms in every bedroom, outside each sleeping area, and on each level of the dwelling. 
• CO alarms outside sleeping areas and on every level containing fuel-burning appliances or attached garages. 
• Combination alarms can satisfy both requirements when properly placed. 

International Building Code (IBC) applies to larger multifamily buildings and may require: 

• Hardwired fire alarm systems with central monitoring. 
• CO detection that annunciates at a central control unit. 
• Building-wide notification when CO is detected in common areas. 

Current Technology Requirements: 

• Smoke alarms must be hardwired with battery backup OR have 10-year sealed lithium batteries. 
• All smoke alarms within a dwelling unit should be interconnected. 
• CO alarms must meet UL 2034 standards and have end-of-life warnings. 

Local jurisdictions may have additional or stricter requirements, so always verify compliance with your local fire marshal or building department before choosing a solution. 

Best Practice for Multifamily Buildings 

For most property owners, hardwired combination alarms with battery backup and interconnection capability provide the right balance of compliance, convenience, and cost-effectiveness. They reduce the number of devices in each unit and streamline testing while meeting code requirements. 

However, consider separate devices in these situations: 

• Buildings with central boilers or shared mechanical rooms. 
• Properties with attached garages or parking structures. 
• Units with multiple fuel-burning appliances. 
• Buildings where optimal placement for smoke vs. CO detection differs significantly. 
• Properties where local codes specifically require separate devices. 

Additional Considerations 

Maintenance and Testing: 

• Establish regular testing schedules (monthly for functionality, annual for professional inspection). 
• Keep detailed maintenance records for liability protection. 
• Consider smart/connected alarms for remote monitoring in larger properties. 

Tenant Education: 

• Provide clear instructions on testing procedures. 
• Explain the different alarm sounds for smoke vs. CO detection. 
• Include information about battery replacement (where applicable) in lease agreements. 

Takeaway 

Both combination and separate alarms can be code-compliant for multifamily properties. The best solution depends on your building's setup, local regulations, maintenance capabilities, and budget considerations. Combination units often provide the most practical solution for smaller multifamily buildings, while larger properties or those with complex fuel-burning systems may benefit from separate, specialized devices. 

No matter which option you choose, the key is ensuring full coverage, proper installation, code compliance, and regular maintenance to protect your residents and your investment. Always consult with local fire safety officials and consider hiring certified fire protection professionals for larger or more complex installations.