An interesting failure mode of the (motor of the) compressor(s), if automatically started with the usual pressure-circuit:

This is not a problem if the power outage is longer (say, 10 sec, enough time for relief from the small tube)


just a ser2net autostarted after boot?) the relay-control HW would be trivial (and stateless) this way.

5V relay (eg. 230V, 10A) might be useful (usually a small PNP inside, activated by pulling input to GND)