Canoeing.com Definition: Personal Locator Beacons, or PLBs, are portable, handheld transmitters that use satellites to send personalized distress signals at emergency frequencies monitored by Search and Rescue teams: 406 MHz and 121.5 MHz. PLBs broadcast a digital signal with personalized information and a honing signal. Activating a PLB allows search and rescue teams to locate the distressed party to within three miles of their exact location, and often launches a rescue in as little as 45 minutes. PLBs are best suited for true emergencies.