1. Add your Hidden Door Sensor to Indigo in the usual manner. Test it to your satisfaction. I suspect that cutting pieces off of it will likely void the warranty, so it’s probably best to ensure it works properly before proceeding.
2. Open the sensor’s plastic enclosure to reveal the circuit board. Remove the battery, then gently pry the circuit board out of the enclosure.
3. Mount the circuit board in a vice. Be sure it’s held firmly in place without damaging it. Move the beeper and the antenna wire out of the way. Using a Dremel tool (or something similar), cut off the metal battery-holder clips. You won’t be needing them, as the sensor will get it’s power from one of the lock’s batteries. Note: do not attempt to simply bend the battery-holder clips out of the way. They are quite rigid, and applying enough force to bend them will crack/break the circuit board and ruin the sensor. Don’t ask how I know this.
4. The clips on the NEGATIVE end should be cut off very close to the surface of the circuit board. The clips on the POSITIVE end should be cut off higher, so that they remain taller than the Status Switch (SW2) soldered to the circuit board adjacent to them. They will serve as support legs to prevent the Status Switch (SW2) from being depressed when you install the circuit board into the MiLocks enclosure. If you cut the clips too tall, the Reset Switch (SW1) will likely be depressed when you mount the lock to your door, as the sensor circuit board will not be recessed deeply enough in the MiLocks enclosure. If you cut the POSITIVE-end clips too short, the Status Switch (SW2) will be permanently depressed when you install the sensor into the MiLocks enclosure, and the sensor will never report any state changes. Notice the very small gap between the Status Switch’s actuator and the surface on which the modified circuit board is resting. I suggest cutting the POSITIVE-end clips longer than necessary, and then gently filing them down to achieve the desired results, as pictured.
5. Solder a small wire (I used solid-core 22-gauge telephone wire) to the Status Switch (SW2), as pictured. With the circuit board oriented such that the Status Switch (SW2) is on the left side, facing up, the correct pin is the top-right one, just below the text “SW2” on the circuit board. This is your signal wire that will be used indicate the locked/unlocked status of your lock. The wire need only be about three or four inches long. You’ll cut it to length later.
6. Solder positive and negative power wires onto the other side of the circuit board. Note that there are three large (relatively speaking) lugs you can choose from for each wire. Note also the orientation/direction of each wire relative to the circuit board — it’s not critical, but it makes routing the wires in the MiLocks enclosure a bit easier.
7. Remove the metal backing plate from the lock assembly by first removing the three screws from the holes indicated.
8. Drill a small hole through the plastic enclosure at the location shown. It’s diameter need be no larger than required to pass the positive power wire you previously soldered to the sensor circuit board. Ensure that the hole is positioned just beneath the base of the right-most spring at the top of the lock’s battery compartment (right-most once the entire lock assembly has been flipped over to reveal the battery compartment, as pictured in the 2nd shot, below.)
9. Place the sensor circuit board in the cavity on the opposite side of the lock’s battery compartment, as shown. I used a piece of black electrical tape to hold it in place. Position the beeper and the route the antenna wire so they’re of the way.
10. Route the positive power wire through the hole you drilled in step 8. Cut and strip the end of the wire such that the bare end sits neatly in the bottom coil of the spring, as shown. Optionally, place a single AA battery in the battery compartment to compress the spring and hold the wire in place. This is not the battery that will power the sensor (the one to it’s right will do that later) so there is no danger of prematurely applying power to anything.
11. Cut, strip, and solder the NEGATIVE wire on your circuit board to the solder bead on lock’s black ground wire, as pictured below.
12. As in Karl’s updated instructions, use a diode to connect the signal wire (step 5, above) to the lock’s circuit board. Connect the diode's cathode lead to the lock’s circuit board at the header connector for the orange wire coming from the lock’s limit switch — the one that is not connected permanently to ground, i.e. the one that is switched to ground only when the lock is locked (see photo, below and refer to Karl’s updated instructions, linked above.)
(Note: Rather than solder the diode’s cathode lead to the lock’s circuit board, I cut the lead at a 45-degree angle to create a sharp point on the end and inserted it into the open end of the header connector. It makes for a solid, reliable connection without soldering. I used several pieces of black electrical tape to prevent any bare leads from touching anything inside the enclosure).
13. Solder the diode’s anode lead to the signal wire you previously soldered to the sensor circuit board.
14. Final installation. I used plenty of black electrical tape to ensure that none of the bare leads are touching anything.
