Ford 2003 Mustang Owner's Manual page 64

Controls and features
To replace the battery:
1. Twist a thin coin
between the two halves
of the transmitter near
the key ring. DO NOT
TAKE THE FRONT
PART OF THE
TRANSMITTER
APART.
2. Place the positive (+) side of new battery in the
same orientation. Refer to the diagram inside the
transmitter unit.
3. Snap the two halves back together.
Replacement of the battery will not cause the
remote transmitter to become deprogrammed from
your vehicle. The remote transmitter should operate
normally after battery replacement.
PERIMETER ALARM SYSTEM (IF EQUIPPED)
The perimeter anti-theft system will help prevent
your vehicle from unauthorized entry.
If there is any potential perimeter anti-theft problem
with your vehicle, ensure ALL key fobs (remote
entry transmitters) are brought to the dealership, to
aid in troubleshooting.
Arming the system
When armed, this system will help protect your
vehicle from unauthorized entry. When unauthorized
entry occurs, the system will flash the headlamps
and/or parking lamps, and the theft indicator lamp
and will chirp the horn.
The system is ready to arm whenever the ignition is
turned OFF. Any of the following actions will prearm
the alarm system:
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