By Sam Holland, co-founder of informal

Why this crossed our desks: After seeing the complicated design of the SimpliSafe Water Sensor, the simplicity of the Temperature Sensor was calling to me. I’m impressed that the entire device is secured with a single thread-forming screw, allowing fast and efficient assembly.

The holes on the side of the device were puzzling me, as they add complexity to the injection-molded housing. I later realized that they allow for sufficient airflow to the device to accurately measure temperature. Neat!

I also really enjoy their use of a mid-mount tactical switch and the way the PCBA is secured to the housing. This is a very well-designed product.

Table of Contents

Temperature sensor overview

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Unlike the water sensor, the temperature sensor is designed to adhere or screw to a wall.

• The front of the device is pretty boring, featuring a pad-printed logo (1) and that’s about it!
• The back of the device has a mounting plate (2) with a 3M command strip attached (3). This is a smart way to deal with wall mounting and prevent damage when removing the device too.
• The mounting plate installs to the rear housing by pressing into an opening, then sliding upwards with a nice satisfying click.
• The top of the device has a pairing button (4) and some slots on the left and right sides (5). I was initially perplexed why these slots were added, but then I realized they provide airflow to the sensors inside! </aside>

Under the mounting plate

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• Removing the mounting plate exposes the replaceable coin cell battery (1). This uses a similar snap hook and cantilever design as the water sensor. If it ain’t broke, reuse the CAD!
• We can also see some certification markings and disposal instructions molded into the top of the rear housing (2). This is a low-cost way of adding text to parts.
• The mounting plate has a few nifty features: two countersink screw holes (3) for fastening the plate to the wall and a slot to make it easy to access the pull tab of the command strip (4). This is a great little design element.
• We also spied a few small plastic ribs on the rear housing (5) and these four surfaces make contact with the mounting plate to help control the distance between the two parts and ensure they slide smoothly by reducing the contact area. Very smart!
• A single screw seems to hold this all together (6). </aside>

Opening the housings

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• After unscrewing the thread-forming screw and gently prying, the two housings separate easily, exposing the sensor PCBA (1).
• The four locating posts for the PCBA (2) aren’t symmetric , which ensures that the circuit board can only be installed in the proper orientation.

This is called poka-yoke, but I call it “idiot proofing,” making sure there’s only one way to build something. This is a very important feature to implement!

• A few locating posts (3) help align the housings and hold the PCBA in place. Everything is held together with a single screw boss(4). </aside>

Housing details

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• The housing is also kept together using two snap hooks (1) molded into the rear housing, which engage with two features in the front housing (2).
• Four vertical ribs (3) prevent dust and debris from entering the airflow holes on the sides of the device (4).
• The hook features and holes are all formed using off-axis injection molding that allow for undercuts.
• The holes on the perimeter are formed using slides, which are sections of the mold that slide perpendicular to the mold axis.
• The snap hooks are formed using a feature called a “**lifter,**” which pivots out of the way. These are usually actuated by the separation of the mold. </aside>

Rear housing details

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The rear housing is where all the magic happens on this device.

• We can see the four slots for airflow (1) on the left and right sides of the device.
• Four mounting features (2) are formed using shutoffs in the injection-molding tool.
• The front housing is attached using two snap hooks (3) and a single screw (4) hole.
• A hole in the top (5) is for the pairing button, which slides using a small guide rib (6). </aside>