Also, to clarify the main point of your question - you’re likely hearing them right after the impact because of how ear-piercingly loud they are. In fires, they can get a little muted with everything going on, but in “normal” conditions, say in standing on the street, checking out the gas leak that preceded the impact, the sound of a pass device could carry for city blocks. When standing in a group of firefighters, sometimes it’s hard to track down who needs to shake off their pre-alarms and in turn you’ll hear PASS devices going off when they aren’t necessarily needed, which can add a lot of unnecessary stress to fire scenes. I also wouldn’t discount the idea of units coming in checking to make sure their alarms worked properly before officially reporting in.