Safe Crate  comes with two devices , Device 1) Smoke / Fire and carbon Monoxide  detector equipped with bluetooth , peel and stick backing for mounting purposes or a small eye at the top for it to be screwed or a hook to hook to cage ,  and powered by a standard 9 volt replaceable battery.. This is just a detector  there is not a sounding alarm on this device..  Device 2 )  The 12 volt lock solenoid box is also equipped with bluetooth , two switches  one to open / close the door , two to kill communication between the detector and the blue tooth receiver in the lock solenoid box  , and a 12 volt rechargeable battery for a power source that is tapped into a 12 volt relay thats wired to a 12 volt lock solenoid… When the detector  detects smoke / fire and or carbon monoxide  it will send a signal via blue tooth  to the blue tooth receiver  located in the lock solenoid box  which will then trip the 12 volt relay and close the circuit  to  send power to the 12 volt lock solenoid to open , freeing the crate door to open automatically by a spring that is simply  placed on the door hinge side to make the door have just enough  spring in it to open on its own freeing the animal…