All these avalanche beacons shown here are for finding people. What do you call the units that send the signal when someone is trapped by an avalance?

Hi Linda, For clarification, all avalanche beacons send a signal during the standard (transmit) mode, and will "beep" for hundreds of hours on new batteries when they are turned on (replace the batteries once they show any signs of weakness, usually on a meter on the device). It takes a conscious effort to switch the beacon to receive, so that it cannot happen accidentally. The device then stops transmitting the signal, and operates in search mode. It is important for everyone in the area to understand how to switch to search mode immediately in an emergency (someone is caught in an avalanche) so that there is not an extra signal being picket up by the searchers. It is also important to understand how to switch back to send (transmit) in case of a second avalanche during the rescue. No matter what beacon you choose, be sure to practice with it in as many scenarios as possible: single burials, deep burials, multiple burials, etc. There is a lot of educational information, but only real life practice (in the snow, in the forest, on steep slopes, near cliffs, and other challenging conditions, before you are ready to ski into those circumstances). Also, find partners who are willing to practice with you until everyone can consistently find and uncover a beacon in a stuff sack (probe practice too!) within 5 minutes. Then go charge those big lines! Avalanche education courses are super informative and well worth the $$$. Have fun and make practicing like an adventure game (it can be easy to spend hours or a full day doing it when conditions aren't great for skiing). If you need inspiration to practice, read accident accounts at: http://www.avalanche.org/accidents.php?date=2008-2009

transceiver = transmitter + receiverAll modern avalanche transceivers operate using the same radio frequency...so all can "hear" one another when a search is required.