The Garmin Foretrex is a series of wrist-mounted GPS devices. They do not support mapping, but can record a tracklog and waypoints.
The 101 uses 2 AAA batteries, the 201 has a built-in rechargeable lithium-ion battery, otherwise they are identical.
Uses 2AAA batteries, has a high sensitivity reciever, and can record 10,000 points in the tracklog.
Work as USB Mass Storage devices. The tracklog and waypoints are saved in the file Garmin/GPX/current/Current.gpx
The 401 has an electronic compass and barometric altimeter, and can connect to a Garmin heart rate monitor or cadence sensor. As of firmware version 2.30, the heart rate / cadence data is recorded in the GPX track.