A single CR2032 battery, we recommend Energizer(tm).
How does the unit power on?
The unit will power on when you apply the electrical circuit to test to the brass terminals. If it does not power with a red/green continuity indication the circuit may be completely broken or the battery flat. In this case pressing the button once will force a wake up of the unit allowing you to confirm the CFCT-FOB is functioning. If the red LED continues to show when the circuit is attached then the circuit is completely broken and needs investigation.