In Ben’s presentation he (and his friends) had a variety of TNCs (terminal node controller – but think ‘modem’) in a variety of sizes, capabilities and cost.
Trackers are (typically) transmit-only TNCs that don’t receive messages, they just transmit a message, typically a GPS-derived location, to the digi or a command post.
Hams running in a marathon with other runners to indicate the start and end of the pack would be an application of these units.
You’d need :
Check these out from Byonics
a) a GPS receiver : Byonics GPS-2 $69
b) the Tracker : Byonics TT3 $42
c) a small radio : Hamfest
Byonics makes this “ready to roll” also:
Scott / KD5NJR