There is a lot of residential work thats not just 0V or 110/120V. If you are doing any work on your HVAC system you will see 24V, 0-10V analog signals. And you can’t just turn the furnace or AC off if you want to troubleshoot some electrical issues.

Prop firearms are not really consumable items. They are just rented over and over again by production companies from rental companies. And when they break, the rental companies would first repair them before buying new ones. They could be decades old and have been repaired over and over.

I assume the shitty reliability of prop guns has more to do with their age and how much they are used rather than low manufacturing quality.

In most newer cars (not even that new, pretty much everything in the last 20 years) computer only fully shuts off if the battery is disconnected. It continues to monitor the car even with the engine off and the key out.