Audio Alarm

Noise is the whole point. Give the alarm power and it plays a loud warning for as long as the power stays, which makes it the simplest raid alert you can build at a Level 1 bench.

Its usual partner is a seismic sensor. The sensor's game text says it picks up vibrations and outputs a different power value for each type of explosive, which is exactly what you want to hear about. Power the sensor from a small rechargeable battery or your main circuit, wire its output into the alarm with the wire tool, and put the speaker in the core where everyone crafts.

Then it pays off like this: you are deep in a building session with music on, and on the far side someone is stacking satchels on the honeycomb. The first explosion sets the speaker off in the next room, and the whole group is kitted up while the raiders are still a wall out.

The limit is plain. A speaker only warns people who are there to hear it, and the neighbours hear it too. For the hours you are away, send the same signal through a broadcaster to an RF pager instead.