Are you using a DVOM set to mA in between a battery post and it's
terminal, or an inductive clamp style ammeter?  Are you certain it is
accurate?

Yes, the alarm, if aftermarket, should be fused.  Look for the alarm
module usually found under the dash, and there will be several inline
fuse holders wired to it.  Pull all of these fuses.

Keep in mind you need to keep a DVOM style ammeter in place at all
times during the test.  If you break it's connection the ECMs will have
to go through their power cycle again when you hook it back up, and all
capacitors will have to recharge.  If your meter automatically powers
down (a common battery saving feature) then it may break the connection
that way as well.

Toyota MDT in MO

Some of these cables corrode internally and you may not see it unless you
can skin back the
rubber and examine.  And, battery cables and their contact points also need
to be clean on both
ends for them to work correctly.

100 ma is a little high, but as was previously posted, this should last
several days.

Try removing the wire that goes from alternator to battery and see if the
drain goes away.
If so, maybe there is a high resistance short in a diode in the alternator.
This will not only
decrease your ability to charge, but can also give a discharge path to
ground. ( If your normal
static drain is 50 ma, then your additional resistance path to ground would
be about 270 ohms)

Batteries that are more than a year or two old may also fool you.  Have you
had it checked?
Is the electrolyte up to level?  Poor battery test procedures can often give
a clean bill of health
to a crappy battery.