Our geiger counter is designed with the prepper in mind. It works on both AC and DC voltage and can work on external batteries (including mobile phone power banks and cordless powertool batteries up to 36V). The builtin voltmeter gives you a visual indication of the applied voltage while the over-voltage protection protects the unit from applying too much voltage. The unit has a short circuit protection, automatic and resettable fuse and even works with battery wires connected in reverse. This makes the unit very user friendly and allows one to power the unit from a multitude of power sources.