I unplug power equipment before changing bits and blades. Do you?

I ALWAYS unplug the circular handsaw , and often unplug the smaller electric drill motor, and always unplug the larger drill motor. But that is quite a bit different.

 

I have an old garage with a pull up door where I store some expensive bikes. It's a pain in the neck to lock it and even when I get it locked, the padlock can easily be cut with boltcutter. I'd like to put a magnetic contact sensor on the door, such that when it is opened between the hours of about 10pm and 7am, a loud alarm sounds and strobe lights flash. Our bike thieves are not particularly sophisticated. I'm sure the alarm and strobes would scare them off. Plus our bedroom is close to the shed.

I'd like to be able to power the alarm by plugging it in to an outlet in the garage with a plain old analog timer that will supply power to it between 10pm and 7am. I don't want anything battery powered or wireless. I don't want a smart system that connects to my phone. I want to be able to set it up, set the timer and forget about it.

I can't seem to find any ready-made products online that do this and I have no idea what to Google to get some guidance. It would be great if someone could tell me what terms to Google or what products to look up. I'm pretty handy but haven't done any electrical. Thank you in advance for any help.

What if you have a power cut , you need a battery back up ideally ...

 

There are padlocks around that will confound bolt cutters, they are often used on self-storage units. And there are cheap junk padlocks made of cast pot metal that I could break with my bare hands. Certainly a good padlock does cost more. And I have been locking my bikes in the garage with a chain and padlock on the rol up door for 25 years. and on the swing-up door for 15 years before that. That small inconvenience does not come close to the inconvenience of having my stuff stolen. So it is a trade-off. And if the power wires to the garage are buried then it is not likely that they would be cut. And a mains powered alarm that lights lights and makes lots of noise if opened when the time switch is on will certainly give the bad actors a reason to run. AND if there is a second unlock needed after the door is raise a foot and the alarm is triggered, it is very unlikely for a smash and grab to succeed. The secondary locking does not even need to be an actual padlock, just a carabiner to an eyebolt on the hidden side of the door, unseen from the outside, with a visible padlock to an eyebolt in the floor.