Car Alarms: 1998 mustang anti theft alarm, valet mode, dash area

Question
Hi we are having a problem taking the battery out of our car without the alarm going off

Answer
Seems the system is reset, and needs
to be done again.

Probably when, or if it lost power.

Right, Ok, try this.
Put the key in the ignition, and turn forward
all the way just before cranking. Then within
5 seconds, press and hold in the valet/override
button, found under the dash area, usually to the left
of the leg, drilled into a plastic panel.
Might even be part of an on glass antenna
in the windshield if it's a remote starter,
until the installed LED (the blinking light)
in your dash area goes off, and the siren chirps twice.
(Your valet switch might be the toggle (on/off) type.
in this case, key on, flip switch in opposite direction,
key off.)

This should reset the alarm and allow you to
go on your way.

Just Repeat these steps to place it
back to valet mode.

That should do it.

Good luck.

ALARMTEK