GMC Sierra Classic 2007 Owner's Manual page 114

Q
(Lock): Press this button once to lock all of the
doors. Pressing lock again within three seconds
may cause the horn to chirp for lock confirmation.
You can choose different feedback options for each
press of the lock button. See "Lock Feedback" and
"Unlock Feedback" under DIC Vehicle
Customization on page 279 for more information.
L
(Panic): Press this button to sound the horn
and flash the headlamps and taillamps for up
to 30 seconds. Panic can be turned off by pressing
the button again, by waiting for 30 seconds, or
by starting the vehicle.
Matching Transmitter(s) to Your Vehicle
Each RKE transmitter is coded to prevent another
transmitter from unlocking your vehicle. If a
transmitter is lost or stolen, a replacement can be
purchased through your dealer. Remember to bring
any remaining transmitters with you when you go to
your dealer. When the dealer matches the
replacement transmitter to your vehicle, any
remaining transmitters must also be matched. Once
your dealer has coded the new transmitter, the lost
transmitter will not unlock your vehicle. Each
vehicle can have a maximum of four transmitters
matched to it.
114
Battery Replacement
Under normal use, the battery in your RKE
transmitter should last about two years.
You can tell the battery is weak if the transmitter
will not work at the normal range in any location. If
you have to get close to your vehicle before the
transmitter works, it is probably time to change
the battery.
Notice: When replacing the battery, use care
not to touch any of the circuitry. Static
from your body transferred to these surfaces
may damage the transmitter.