This is the MYLAPS Personal RC4 Hybrid Direct Powered Transponder.

Features:

• Half the size, half the weight of the original
• Low voltage operation: 2.8-16 Volt compatible
• Transponder and transponder holder are individual parts, so you can easily switch transponders between different cars (extra holders sold separately).
• Better quality cable (PTFE) that is fuel resistant
• 1-4 cell LiPo compatible
• Fully hybrid:
• 100% compatible with RC2/RC3 Timing Systems (previously AMBrc)
• 100% compatible with RC4, and ready for the future

Specifications:
Dimensions (excluding holder) (LxWxH): 16x19x6mm
Weight: 4.7g (including holder)
Operating voltage: 2.8 - 16.0 V
Power consumption*: 19 mA
Wire isolation**: PTFE
Quick change holder: Yes
Connector: Generic receiver 3-pole

* Measured at 6.0 volt (receiver output)
** Gasoline/Nitro-methane resistant, no aging  

NOTE: See image below for a list of transponders and compatible MYLAPS decoders.