WIRED OR WIRELESS CONNECTION - This smoke and carbon monoxide detector can be hardwired or wirelessly connected to up to 12, so when one alarm is triggered, they all sound and notify everyone of the emergency. | HARDWIRED AND 2 AA BATTERY BACKUP INSTALLED - The combination of smoke and carbon monoxide detectors can be connected for use in addition to the 2 AA battery backup. When the power goes out in your house, the detector will still keep you safe. | 2 IN 1 PROTECTION WITH UNIQUE VOICE ALARM - This combination smoke and fog detector with dual sensors detects smoke and carbon monoxide hazards in a single unit, providing an audible warning in excess of 85 decibels. In addition, the unique voice alert lets you quickly understand whether smoke or carbon monoxide is present, allowing you to avoid scenarios in a more organized manner. | SELF CHECK FUNCTION - This SITERWELL smoke detectors and CO combination detectors have a self-check feature that replaces manual testing. When a detector fails to work, it will notify you as soon as possible to ensure you are effectively protected. | HIGH QUALITY ASSURANCE - The combination detector has a 10-year sensor life and a reliable, high-performance chip to provide you with powerful protection. Products meet UL 217 and UL 2034 standards to ensure peace of mind.