The premise behind how this works is pretty simple. The magnetic alarm runs off of a reed switch that connects every time a magnet is near it. So if we connect this switch to the up arrow key on the keypad, then every time a magnet passes by, the switch will connect and the button will be pressed. So if you have Google Maps open, pressing the up button will propel you forward.
Step 3: Solder the alarm to the keypad
Open up the keypad until you see the circuit boards that comprise it. Find which circuits connect to trigger the up arrow key (or key 8) and connect the wires to it. Since there are thousands of different keypads available on the market, yours will not look exactly like the one I used in this example. But in my case, I was able to find that circuits 4 and 3 (shown in the graphic below) connected when the up arrow key was pressed. So I traced those circuits back to the main logic board and soldered the alarm wires to them, so that when the alarm is tripped, it triggers the up arrow.
Step 4: Test the rig
Once you have the wires connected to the button, put everything back together. You may need to cut some of the plastic casing in order to accommodate the extra wires we added. Now plug the USB keypad into your computer and open up maps.google.com and make it full screen. Then you'll need to hit the numlock key on the keypad to turn the number lock off. Now whenever you pass a magnet by the alarm switch, the map should move forward.