Marvin KE6HTS has some small beacons designed for ARDF
that can be used in a number of ways:http://www.rain.org/~marvin/
Another one is the N6BG "pocket fox":http://www.byonics.com/pocketfox/
I've also used a standard HT on low power. On one old
crystal-controlled HT that I have, the low power switch
simply added a resistor to the circuit, so I replaced the
resistor with a trimpot that allows me to adjust the output
You can reduce the power out of an HT by putting a dummy
load on the output - there will still be some radiation
from the case. If that isn't enough, put a BNC "T"
connector on the antenna jack with a dummy load on one
side and a short (6 inch) whip on the other.
If you are using an offset (or "active") attenuator, or
even a cardboard tube covered in tin foil, you should be
able to hunt a 1-watt transmitter up close enough to find
it when it isn't too well hidden.
Generally most hidden transmitters make use of a standard
HT connected to an external battery and some sort of
ID'er/controller/noisemaker, such as the PicCon from
). Personally I use the Montreal
Controller circuit from VE2EMM because I can build them
for about $15 each (which is important when I need a
set of 6 with backups.)http://www.qsl.net/ve2emm/
Radio Shack carries (or used to, anyway) a voice recorder
chip that makes a simple ID'er, but I don't know of any
built commercially. Similiarly it isn't too difficult
to build a simple 2m crystal-controlled transmitter, but
often I can find old working HTs at a hamfest for $25
which makes it hardly worthwhile using anything else.