If I recall, these have some kind of tube that is plugged on one end with some time-release mechanism, perhaps a material that slowly dissolves in the water. Ev

If I recall, these have some kind of tube that is plugged on one end with some time-release mechanism, perhaps a material that slowly dissolves in the water. Eventually water enters the tube and equalizes pressure on both sides, causing it to detach. This allows them to recover the beacon and make another deployment.