Modify $15 SimpliSafe Entry Sensor As a Wired Switch

The SimpliSafe (SS) security system consists of a wireless hub controller and a number of battery-powered wireless sensors, all communicating over a Z-wave network. One sensor in particular is very inexpensive, the $15 "Entry Sensor" wireless magnetic switch. The sensor consists of the sensor module and an external magnet, which triggers a normally-closed magnetic reed switch inside the sensor module. You stick the sensor on a door or window frame, and the magnet on the door or window itself, and as long as the distance between them is an inch or so or less the switch remains closed.

Alas, there is no provision for attaching a wired dry-contact switch. Having this module include wired switch contacts would be a boon to SS customers. You could implement a wireless doorbell, attach existing magnetic, motion and smoke detectors to the SS system, and create multiple-position sensors (to permit a closed and half-open window, but not a full-open one, for example).

Modifying the SS Entry Sensor turns out to be pretty easy. The first one took me a while, to best determine wire routing outside the sensor module, so I've documented the process in this instructable.

This takes a knack the first time you do it. There are two covers on the back of the module. The first one simply slides off, and covers the battery compartment. It also has a 3M adhesive strip fastened to it. Remove this cover and take out the battery if installed.

Next you have to remove the inner cover. You do this by prying at the three latch indentations with a flat blade screwdriver. This took me a few tries before I figures out this technique: use a large flat-blade screwdriver and pry it in toward the center of the module. Each corner should pop out in turn. You then have to fiddle with it a little to get it out the rest of the way.

Before you can remove the circuit board you have to pull out the battery contacts. Start with the contact on the long wire, at the end of the module. Use a needle-nose pliers and wiggle the contact back and forth to work it out. It's just a friction fit. As soon as this contact is out, the circuit board will become free at one end.

Use the same technique on the mid-case battery contact. Once it is out, you can gently pull out the circuit board. My board had holes for screws, but no screws were installed, so it was entirely friction-fitted. Some might have screws, however, so check for those and remove them if necessary.

The bare board appears in the picture above. The thin glass tube is the magnetic reed switch, and the metal hoop on the bottom of the board is the Z-wave antenna. Take care not to bend the LED leads, as the LED must line up with its exterior opening during reassembly.

Set the board aside for a minute and proceed to the next step, modifying the case to provide a wiring path.

You need to make two notches through which you'll route the wires outside the module case. The first notch goes in the inner cover, marked in red in the photo above. Simply clip out a small notch with a diagonal cutter and pull out the plastic with needle-nose pliers.

Make a similar notch in the module outer case right at the end of the module serial number, also marked in red in the photo above. Take care not to obliterate the serial number label.

Head on to Step 3.

I used a single twisted pair from an ordinary solid-core Cat-5 Ethernet cable (commonly called "riser cable"). You could use stranded wire as well, although attaching is a bit trickier. Solid copper wire stays where you put it, making assembly easy.

Start by measuring a length of twisted pair (I recommend at least a foot) and then cutting the two strands in an offset as shown in the first picture above. Then strip the wire and loop each piece around a lead wire on opposite sides of the magnetic switch. You'll solder these in the next step, so a strong mechanical connection isn't needed. Route the wires along the board toward the right-hand end (with the battery cutout on the left).

IMPORTANT NOTE (9/16/2016) ! Several people have emailed me indicating that they have cut the leads to the magnetic reed switch, or what they thought was the reed switch. You don't need to do this, and I suspect you might cause problems. One person misidentified the antenna hoop (the large-gauge silver wire U on the same side of the board as the LED) as the magnetic read switch and soldered their external relay to that. Needless to say, that won't work either. The reed switch is the glass tube on the top side of the board with all the other parts. DO NOT REMOVE IT.

Proceed to Step 4, soldering.

This is a very basic soldering task. The magnetic switch is not very heat sensitive, so no heat sink is necessary. Just apply the minimum amount of solder necessary for a good mechanical connection. Take care not to melt the rubber pads on the board, which seem to provide cushioning.

You're now ready to reinstall the board. This is the reverse of the dis-assembly process: install the mid-case battery connector, seat the board, and finally install the end-case battery connector.

Seating the board requires one trick: lining up the LED with it's opening in the plastic housing. I've done a number of these mods now, and the easiest way for me is to have a light behind the module so that it shines through the LED hole, then line up the LED so that it starts into the hole before you get the board fully seated.

Note that if you do the board re-seating before installing the mid-case battery connector, you'll have to start over. The wire on the mid-case connector is too short to install it once the board is fully seated.

Step 5 is to test the module before you get it all reassembled.

Test by reinserting the battery and waiting a minute for the module to sync with the SS hub. The LED flashes a couple of times once this happens. Then test the module with the magnet, just to make sure the magnetic switch still works. The SS hub should emit a chime when you open the switch by removing the magnet. Now repeat that test using the wires: short them together, then separate them. The chime should sound.

If either test fails, investigate. I has one instance where the wire I was attaching had a break under the insulation. It's a lot easier to fix that now than after everything is reassembled.

Replacing the covers is straightforward. First insert the inner cover, sliding the side with two latches under their tabs first by angling the board in, then pressing the board down on the third latch. Make sure the wire is routed through the notch you cut earlier.

Then route the wire through the second notch and replace the battery cover by sliding it on. The module is now ready to use. It might be a good idea to run one more test before you put it into operation.

Attach the wires any kind of dry contact switch, such as a traditional normally-open doorbell button. When
the button is pushed and released, the SS chime will sound. Never connect the module to any kind of wires that already have power on them, as the module itself is already supplying power to the magnetic reed switch. Any external power is likely to destroy the SS sensor electronics.