Ademco alarm systems are found in many homes and businesses. The steps to reset the code are the same for most models within the brand. If you buy a home and find an existing home security system with Ademco keypads, you can use these steps to find the current "Installer" code, change it if needed, and operate the system until "Master" and "User" codes can be programmed properly.
If the system is currently monitored, call the central station and put the system on "Test." Consider calling your alarm service company, if you have one; they can usually talk you through code changes over the phone.
Find the main alarm panel box. It may be hidden in a closet, or in a utility room. Look for a tan box, about 14 inches square and 4 inches deep.
Open the box using a screwdriver, or with a key. Look for the key on top of the box or with other keys left by the previous homeowner.
Unplug the AC transformer, a 3-inch cube plugged into an outlet. It may be next to the panel, or is often in the garage door opener receptacle. If you can't find the transformer, go to Step 5; otherwise, skip to Step 6.
Use a screwdriver to remove the wire from the screw terminal on the far left side of the circuit board. Don't let this bare wire touch anything else, although it's low-voltage and safe for you to touch.
Remove one lead from the battery, sitting in the bottom of the panel box. Wait 10 seconds, then re-attach the lead.
Re-connect the wire to the screw terminal, or plug the transformer back in, whichever you undid.
Go to the keypad within 60 seconds of powering up the system and press the and # keys at the same time, then release. The keypad should display either "20," or "00." If it does, you are in program mode. If not, repeat the power-down/power-up sequence, and press and # together again.
Press #, then the displayed number, either 2,0, or 0,0. The keypad will display a sequence of four, 2-digit numbers such as "04, 01, 01, 02". Write the number down -- this is the "Installer" code, in this example, 4112. It can be used as is, to operate the system, or used to program the "Master" code. If you want to change it now, press , 2, 0 or , 0, 0, then a 4-digit code of your choice. To exit program mode, press *, 9, 9, and wait a few seconds.
Arm, disarm, and perform all the functions of the system. You are using the "Installer" code; normally, it is used to program a "Master" code and several other "User" codes, but this will at least allow you to use the system.