|While this trap does no damage by itself, its loud sound may bring someone to do damage to you. Of course, you have the option to do damage to those someones yourself.|
An alarm trap is a trap which produces a loud noise (intensity 40, louder than Shatter) when stepped on by either you or a monster, alerting anything nearby. If you step on one, it also afflicts you with the Sentinel's Mark status effect (ignores magic resistance). Like all traps, alarm traps can be set off even by flying beings. After triggering once, they disappear.
Alarm traps cannot be disarmed, but can be silenced. Silence does not prevent the Sentinel's Mark, though.
If an alarm trap is triggered by a being in the distance, you see this message:
"You hear a distant blaring wail to the [direction]."
- If you're travelling through an early floor you've already cleared, find an alarm trap, and need a quick bite, stepping on it is not a bad way to summon any potentially edible opponents to you.
- Being silenced reduces the number of creatures you lure to you significantly; enemies you haven't seen yet are usually asleep, and only the few wandering opponents on the floor will come to you. Of course, if you then proceed to fight them all near unexplored territory, it's possible you'll wake up more.
- Another safer way of getting rid of an alarm trap is to lure an enemy into stepping on it. This will still make a loud noise, waking up nearby monsters, but at least they won't be drawn right to you by Sentinel's Mark.
- Stepping on the trap and then quickly rushing upstairs to a cleared floor will still likely awaken several opponents, but they won't be able to swarm you en masse nearly so easily.
- Quaffing a potion of cancellation removes Sentinel's Mark immediately, and the awakened opponents mostly lose their ability to track you immediately, though these items are somewhat rare.
- If all else fails and you need to make a last stand, you'll usually have a few turns free before the hoard arrives; consider using that time to create a killhole, and don't be afraid to teleport if it's clearly going badly for you; all those enemies clustered around your old location will need a lot of time to catch up with you, during which you might be able to escape the floor or lose the status effect naturally.
Prior to 0.12, alarm traps could activate multiple times before breaking, but they were not quite as loud and did not afflict you with the Sentinel's Mark.