pinger

Short definition from Wiktionary

Noun

1. 1
   A device that emits a short, high-pitched sound burst, such as in sonar or other echo location systems.
2. 2
   A device that periodically emits a signal that can be monitored to permit movement tracking.
3. 3
   A computer program that sends a ping message over a network.
4. 4
   A user of a ping program; one who pings.
5. 5
   An illicit drug, especially ecstasy, taken for recreational purposes.