Duracell Alkaline Security Batteries offer reliable, long-lasting power. The MN21 alkaline battery will give you the power you need for your important electronic devices. Power up important devices, such as your key fob, car alarm and garage door opener. Alkaline Voltage: 12.0 IEC: 3LR50 33 mAh Size (mm): 28 x 10 x10 4 Pack Designed for use in: Car alarm Key fob GPS tracker Child locator.