Pokitmeter does not have an on/off button. When Pokitmeter is disconnected from a mobile device it will continuously run in Discovery Mode, letting other devices connect to it.
Pokitmeter uses Bluetooth Low Energy (BLE), a very efficient radio protocol which uses very little battery power. When in Discovery Mode Pokitmeter uses less than 10 micro-amps, equating to a battery life of up to a year.
If you want to stop Pokitmeter running in Discovery Mode, you should remove the battery entirely.