The following is the text from the Empty Room, Tricks, and Traps document. The additional information is added to increase agency.
Proximity: This trigger is an extremely sensitive device that detects vibrations, most often transmitted through the air. They are generally very sensitive and only used in out of the way places. Note that because they detect vibrations in the air, they are also extremely sensitive to sound. Non-thieves have a difficult time detecting these traps. There is little that you can do to notice this trigger, but the area around a proximity trap has no breeze, is very quiet, and often has either a thick layer of dust on the floor or no dust at all. Disarming it is a difficult and time consuming process - increase the length of time required to disarm a proximity trigger by 10 times. On the positive side, these triggers usually only trigger alarms or summon guardians of some sort.Mechanical proximity triggers are interesting triggers because they often are not directly detectable. The only clues you will have to proximity detectors is that the area is sealed, and appears undisturbed. Even sensitive ones can avoid being triggered by someone who is quiet and walking softly, so approaching and disabling them is possible. The difficulty comes in finding them.
I would generally rule that finding a proximity trigger without triggering it takes twice as long as just searching a square normally. Also, that it can only be done by one person at a time, slowing down the process even more.
Since these are triggered by vibration, be aware of talking loudly or other action the party might take to set it off.
Another way to handle these triggers is to just set them off. Throw a thunderstone down the hallway and cover your ears.
The biggest clues you have in order to detect a trigger of this type are the signs that the area has not been disturbed or visited in a long time. Examples above, such as dust, are useful; other signs of proximity triggers in use include:
- Sagging shelves and furniture or curtains
- Hard stone or metal hallway floors or acoustical ceilings to increase the noise made
- The section of the dungeon is a sealed or is clearly a vault.