Yes. Your system will continue to function while running on the backup battery. The length of battery life is usually around 12-24 hours depending on the strength and age of the battery. Your system will go into a power saving mode to conserve the battery. This includes turning off the keypad until a button is pressed. Be aware, if you have digital phones, your phone lines may not work, preventing your system from communicating. CPI also offers a cellular unit with Real Time voice technology, which does not require a phone in the home.