Three climbers stranded on Oregon’s Mt. Hood after falling from a snowy ledge on Sunday are equipped with Cellular Phones and Mountain Locator Units to aid rescuers.

The three climbers – two women, a man, and a Labrador – are able to maintain contact with rescue officials with a cell phone. The climbers also have at least one mountain locator unit with them to assist rescuers.

Mountain locator units or Personal Locator Beacons (PLB) are lightweight devices that attach to clothing and emit a signal which can help rescuers pinpoint the location of missing or stranded climbers. When activated, the beacons send out a distress signal that allows the beacon to be located by the satellite system. The devices can transmit GPS coordinates in the emergency satellite transmission.

The devices can be rented for as little as $5 at mountaineering outfitters or purchased through outdoor retailers like REI. Groups on Mt. Hood must carry a Mountain Locator Unit and all climbers must sign-out at Timberline lodge before their climb and sign back in upon return.

As rescue teams prepare their evacuation, the climbers are huddled in sleeping bags and trying to stay protected amidst the ferocious wind and blowing snow. Rescue teams make their way to the site, believed to be around 8,300 feet, hoping to beat a snow storm expected later in the day.