You need the whole information to decide what is switched off, but there is enough information to describe it in general terms. The timer is an automatic device used as a fail safe mechanism. The alarm means that something unusual is happening and an alert is sounding or being indicated by flashing lights. So once the fault is detected, something causes an alarm and starts a timer. If a person is not alerted by the alarm and then corrects the fault, the automatic action is to shut down the process after a certain time (which is where the timer comes in).

The timer in the sentence is a device.Meaning the time keeps on runing.Switch off means turning it off.