We have a small shop unit attached to the house, with separate mains electricity supply, and an alarm. The incoming mains is interesting. The incoming mains feeds through a sealed fuse unit, then the meter, then a junction box, where three feeds emerge. One goes to a standard fuse box with on/off switch, and supplies lights and sockets.
The second goes through a second fuse box with one on/off switch and supplies 'data' sockets only. They were for electronic tills etc.
The third goes through yet another fuse box with on/off switch, and supplies the alarm. This third box is metal (the others are plastic), and has a hasp and staple riveted to the case, secured by a padlock such that the switch cannot be flicked off without removing the padlock. I can see why, but it means there is no way to shut off the power to the alarm in the event of, say, fire. Is that usual? No, I have no idea who has a key to the padlock. Possibly issued to the then owner at the time of installation, or held by the alarm contract company?