- The transponder allows the crate to be easily found with the radar installed in the Muscle Car.
- At the start of the Episode Two chapter Under the Radar, the Muscle Car is equipped with a radar in a Resistance outpost located near the Combine Autogun in the Outlands. It is aimed at helping Gordon and Alyx find Resistance supplies equipped with transponders along the road. Thanks to the device, each supply crate appears on the radar screen as a Lambda logo.
- The Transponder is also involved in the Orange Box Achievement "Cache Checker", requiring to find every cache.
List of appearances
- Half-Life 2: Episode Two (First appearance)