[Hardwired interconnection] Up to 12 smoke alarms can be interconnected to cover your entire home. When one detects smoke, they all make a sound to alert everyone in the house, creating an interconnected safety net for your home. [9V Battery backup] Hardwired smoke detectors are equipped with DC 9V batteries. Ensure that all units are always connected and continue to function properly, even in the event of a power failure. Low battery alarm reminds you to replace the battery as soon as possible. If an error occurs, the system automatically triggers the fault mode, prompting you to check the device. [Test Mute button and LED light] It is connected with other alarms. Just press the test/mute button on one of the units to test or mute the entire interconnected system. If the smoke alarm is in normal working condition, the green LED light is always on and the red LED light flashes every 32 seconds [Photoelectric smoke sensor] Based on advanced photoelectric technology, smoke alarms can be more sensitive, fast, accurate measurement of smoke levels. More than 85 decibels of alarm sound, you can more clearly hear the danger coming. [Simple installation] The installation of smoke alarm is very simple. The AC connector is connected only to the mains power and signal cables. (Please connect as instructed) Package Included: 4 packs smoke detectors, 1*dust cover, 1*hard wiring,1*instruction manual,1* 9V battery,1*screws set UPC 768481501668 ASIN B0B4NMTNPX Size 4 pack Alarm Audible Brand Putogesafe Color withe Style Hardwired Interconnected Model Material ABS Item Weight 1 pounds Part Number GS521C-A Sensor Type Photoelectric Manufacturer Siterwell Electronics Co.,Limited Power Source Battery Powered Battery Cell Type Zinc Carbon Item model number GS521C-A Batteries Included Yes Batteries Required Yes Product Dimensions 1.6 D x 5 W x 5 H Item Package Quantity 1