Avalanche rescue involves locating and retrieving people who have been buried in avalanches.
https://en.wikipedia.org/wiki/Avalanche_rescue
Recco reflectors are not a substitute for avalanche beacons. The Recco signal does not interfere with beacons. In fact, the current Recco detector also has an avalanche beacon receiver (457 kHz) so one rescuer can search for a Recco signal and a beacon signal at the same time.
https://en.wikipedia.org/wiki/Avalanche_rescue
These avalanche transceivers have three antennas and support the marking of transmitters during a multiple burial, but they also have one or more additional features.
http://beaconreviews.com/transceivers/transceiver_reviews.asp
In the U.S., 86% of the 140 victims found (since 1950) by probing were already dead. Survival/rescue more than 2 m deep is rare (about 4%). Probes should be used immediately after a visual search for surface clues, in coordination with the beacon search.
https://en.wikipedia.org/wiki/Avalanche_rescue
Discontinued Avalanche Transceivers (click to expand). The following avalanche transceivers have been discontinued. 1 antenna. N/A. 9000. (ARVA). Pros: A very capable single-antenna transceiver in its day. Cons: One antenna, bulky.
http://beaconreviews.com/transceivers/transceiver_reviews.asp
Even small avalanches are a serious danger to life, even with properly trained and equipped companions who avoid the avalanche. Between 55 and 65 percent of victims buried in the open are killed, and only 80 percent of the victims remaining on the surface survive. (McClung, p.177) .
https://en.wikipedia.org/wiki/Avalanche_rescue
Three-Antenna Transceivers with Multiple-Burial Marking (click to expand). These transceivers have three antennas to resolve  spikes  and have the ability to mark (i.e., suppress) a signal during a multiple burial search. In terms of prices and features, these beacons are targeted toward the mid-range market.
http://beaconreviews.com/transceivers/transceiver_reviews.asp
Comfort: The Barryvox 3000 was the smallest avalanche transceiver until the lame, single-antenna Pieps Freeride was released. The 3000 is also smaller than the Tracker3 (which touts that it is the world's smallest avalanche transceiver). Other: The 3000 can be configured to switch between an analog and digital transceiver with the press of the Mode button (the S2 setting, above).
http://beaconreviews.com/transceivers/Specs_BarryvoxOpto3000.asp
(Historically, the chances of survival were estimated at 85% within 15 minutes, 50% within 30 minutes, 20% within one hour). Consequently it is vital that everyone surviving an avalanche is used in an immediate search and rescue operation, rather than waiting for help to arrive.
https://en.wikipedia.org/wiki/Avalanche_rescue
Summary: The now-discontinued Barryvox Opto 3000 is a dual-mode transceiver that starts receiving in analog mode and switches to digital mode as you near the victim. In addition to its dual mode, it has the benefits of two-antenna beacons, offers customization, and is small. This is my favorite two-antenna beacon. Although the Tracker DTS is easier to use (the DTS was the 3000's main competitor), I like the 3000's ability to switch into analog mode and its small size. An earlier version of the 3000 was packaged in a blue case. I'm unsure of the differences between the blue and red models.
http://beaconreviews.com/transceivers/Specs_BarryvoxOpto3000.asp
what is the smallest avalanche beacon?
The Barryvox 3000 is the smallest Avalanche beacon. The Barryvox 3000 is the  smallest avalanche beacon.