So I built a small simple alarm system, with a couple PUT's and NPN's and a Relay. The schematic recommends a 12v battery be used. But I was wondering if I could just use a simple AC-DC adapter instead of a rechargeable battery. I was trying to think as to why use a battery, Im guessing incase the power goes out , the battery can still power the alarm system. But please let me know what you all recommend