What's the point in having an alarm if it doesn't go off in an emergency? Where safety is concerned, compromise is not an option. It's a good thing that Duracell Security have got you covered! This 12V MN21 battery is designed to fit in car alarms, key fobs and other key electrical devices. It is made with the same consideration and attention to detail as all Duracell products, with impressive battery life so it'll still be working when you need it most!