According to the datasheet [1] the transceiver outputs -5dBm. (This is 5dB less than 1 mW.)
This specific device is not analyzed enough to reveal whether or not there is an additional amplifier, which "could" be made from a single transistor and some passives.
Assuming that there is no amplifier, and taking into account the short wire antenna and detrimental environmental conditions, I feel safe guessing the upper bound of useful range will not be more than a 250 m distance. Probably it's half that.
I will also guess that the fixed part (you can call it a transponder or base station) will not have power budget to worry about so it will periodically be announcing itself (you don't want the mobile part to do this because it will consume the battery.) The mobile part will answer when it hears this transmission. If this is true, then a TSCM beginner will be able to play "find the beeper" pretty easily.
