Can you reconfigure the system to work without the glass-break sensor? If so, and the system then functions correctly, you would know the fault lies with the glass-break sensor.
That is a double socket. A plug is what fits into it. If the socket has no power then the circuit breaker at your consumer unit may have tripped (or fuse blown, if it's an ancient consumer unit).
I'd leave it as is if the runners can easily be removed when necessary. Any chance you could modify the CU lid or its fixings slightly to make it removable (but obviously securely closable too)?