Residential Smoke & CO Alarms in Texas: NFPA 72 Compliance & Wiring Best Practices
Residential home fire alarms are required in new construction. In Texas, local jurisdictions commonly adopt NFPA 72 (edition varies). Always confirm the current adopted edition and enforcement with your Authority Having Jurisdiction (AHJ).
Wiring Best Practices (New Homes)
- Parallel 120 VAC with battery backup: Use a dedicated branch circuit and 14/3 (hot/neutral/interconnect) so removing one alarm does not drop power to the others.
- Interconnect conductor: Tie AC-powered alarms together so activation of one sounds all (where required by code and listing).
- Relay modules: Many professional smoke alarms offer listed relay modules that provide a dry contact to interface with professional security/fire panels.
Do Not Daisy-Chain in Series
Series “daisy-chain” wiring of two-wire residential detectors does not meet NFPA 72 intent. A single fault, removal, or service of one device can disable others—creating a life-safety risk and a code violation.
Combo Devices: COSMO & Modules
Combined smoke/heat/CO devices (e.g., COSMO-type) typically require a per-device interface module (e.g., COSMOD-type) when integrated to certain panels. Each detector should have its own module, and modules are then interconnected per the manufacturer’s listing. Do not use a single dual-port device to daisy-chain multiple detectors without a redundant pathway.
NFPA 72 (2022) — Key Clauses (Plain English)
- 29.10.7.8.1: An open, ground fault, or short on wiring to input/output devices shall not prevent each individual alarm from operating.
- 29.11.2.2: A single fault on the interconnect shall not prevent single-station operation of any interconnected alarm.
- 29.10.7.6: When common wiring serves other systems, faults in that other equipment must not interfere with supervision or alarm/trouble operation of the fire/CO system.
Interconnection Limits
- Unsupervised interconnect: Up to 18 initiating devices total (up to 12 smoke alarms).
- Supervised interconnect (where applicable): Many designs allow higher counts (e.g., up to 64 initiating devices, up to 42 smoke alarms)—verify device listings and your adopted edition.
Wiring Method vs. Outcome
| Method | Outcome | Code Risk |
|---|---|---|
| Parallel 120 VAC + interconnect (14/3) | One device removed does not disable others; interconnect works | Preferred / code-aligned |
| Series “daisy-chain” two-wire loop | Removal/fault can drop the entire chain | Non-compliant |
| COSMO devices without per-device module | Loss of pathway can affect multiple devices | Non-compliant |
Quick Planning Tips
- Use listed devices and follow the manufacturer’s instructions for interconnection and modules.
- Keep a dedicated branch circuit for alarms and include battery backup.
- Document device counts vs. interconnection limits and include cut sheets in your submittal.
- Coordinate early with your AHJ to confirm edition, placement, and any local amendments.
Informational only—requirements vary by jurisdiction and adopted NFPA edition. Always verify with your AHJ and the current code.
Need help designing a compliant residential system or tying AC alarms into a monitored panel? Explore our Fire & Life Safety services or request a consultation.