Distress pulser

The distress pulsers are two quest and junk items in Fallout 4.

Gameplay
A device used by the Brotherhood of Steel to mark specific locations, or in the event of an emergency where a soldier or squad may be downed and in need of assistance. When active, it emits a series of blips to any device capable of picking up radio frequencies, which become clearer as the receiver travels closer to the source.

Crafting
The distress pulsers obtained during the quest The Lost Patrol can be broken down into their individual components for use in crafting:

Locations

 * One is located in the National Guard training yard, near the corpse of Tara Astlin.
 * South of Med-Tek Research, in a destroyed building near the corpse of Knight Varham.
 * In the Revere satellite array, in a small shack built on one of the southern satellite dishes.

Related quests

 * The Lost Patrol
 * Liberty Reprimed

Bugs
If a distress pulser is dropped on the ground in a settlement and then scrapped using the settlement building screen it will permanently emit a distress signal. It will also continuously emit a signal if it is used to build modifications, so the only way to remove the signal permanently is to sell it after finishing the quest.