Calibrationless operation method

A system comprising:

• a first sensor to be installed inside an underground vault;
• a second sensor to detect a different property than the first sensor and being complimentary to the first sensor with respect to a particular conclusion;
• and
• a system controller comprising at least one processor connected to memory storing instructions executable by the at least one processor, the instructions, when executed by the at least one processor, causing the at least one processor to (a) obtain a first sensor reading from the first sensor, (b) obtain a second sensor reading from the second sensor, (c) determine an alarm state based at least in part on the first and second sensor readings, and (d) notify a user of the alarm state.