Allows for self-revive when downed.  Larger version of the travel-size Self Rez.
 
The medium-sized version has the following additional features:
Round storage compartment designed for an Apple AirTag
Tight-fitting clamshell closure*
 
*Opening requires moderate prying with a flat tool, such as a screwdriver.  This is to ensure contents remain secure, and is intended to only be opened occasionally.