Smoke detector - Savety shut down Printer

This is a project for every printer and every printer should have it. Also this here is more about the project then for the printing parts.
I read some stories the printer burns down or the electric burned out. To try to avoid a bigger damage as the printers most of the time are in
action without supervision, it's just a question of security to have a smoke detector on it.
This version is low cost and not too difficult to build - even for beginners.
Of course there are many stuff on it what can get improved (electric and programming). This was just a quick project, but it still works fine.


What does it do:
- there are smoke detectors on two side (ANET A8). One for the power supply and the other for the electric main parts
- if one of these detects smoke it cuts of the main power supply with a relay.
- the 9V battery keeps the detectors and the display running and shows an alarm.
- there is also a stopwatch on it for personal use as you want (measure the time of printing