That makes the build much simpler. Revised design: Mean Well DIN-rail PSU fitted by the client’s electrician, my box is 5V only, the MQ-4 is gone, and the certified detector they already had (turns out there was one, nobody had wired its relay to anything) feeds an input. Telemetry is gas_alarm and lockout as booleans plus temp_c, with a Critical alarm rule on gas_alarm == true. Much less for me to worry about.