Podcast: Why there were 56 OT vulnerabilities this week – Stacey on IoT

First, I congratulate Greg on knowing the difference between “occupancy sensor” (someone is in the room), “presence sensor” (Greg is in the room), “motion sensor” (something moved in the room) and PIR sensor (something warm just moved across the sensor’s detection field). Bravo!

While I agree with Kevin and Stacy that much better and more interesting occupancy sensors are likely to be available in about two years, there are some other options available now that might help depending on the exact use case. I’m going to limit this to discussion of options that would work with HomeKit, but there are additional devices for other platforms


If your goal is to know that someone is lying in bed, sitting on the couch, or sitting in a specific chair including an office chair, you can often do that very effectively with a pressure mat. There are a whole bunch of DIY project reports on making these smarter at places like Instructables, but the basic approach is always the same

A) purchase a pressure mat. These come in all different sizes, for a couple of bucks for one that can measure an ounce or two to $ 75 or so for one that knows when a car is parked on top of it. This is basically two pieces of rubber or fabric which close a circuit when they come together, and which are calibrated so that a specific weight will put enough pressure on the mat to make the two pieces contact each other.

You find these in all kinds of crazy places. At Maritime supplies where they are used as a “doorbell“ for a houseboat. (When somebody steps on the mat, a circuit is completed, and a chime can sound). At medical supply houses where they are used for monitoring patients getting out of bed in the middle of the night. Robotics supply companies where they are used for fun projects like knowing when your drone has parked itself.

This part itself doesn’t have a radio inside it. It’s just the mat piece.

B) Now wire that pressure Mat to a smart open / close sensor so that when the pressure mat circuit closes, the smart sensor will report the change in state. The aqara sensors are popular for these because they’re cheap, but you can do it with most HomeKit compatible sensors, including Eve. (in order to work with HomeKit, the aqara sensor also requires an Aqara hub.) The exact details will depend on the model sensor, but you should be able to find that information

Here’s just one example, but again, lots of people have done this with lots of different devices. It’s just a way of adding a radio notification to a pressure mat.

Meet the Aqara pressure pad (DIY idea stolen from a Home Assistant article). It works surprisingly well. from HomeKit

So if the purpose of your occupancy use case is to know that someone is sitting or lying still somewhere, a pressure mat can work well.

If you just want to buy one that works out of the box and not mess around with wiring and taking the sensor apart, you can use Withings Sleep mat, Connect it via IFTTT to trigger an inexpensive Meross smart plug, and use the Meross plug to bring the state change into HomeKit. That would cost a lot more, and it is cloud-dependent because of the IFTTT step, but it’s pretty easy to set up, and works well for a bed or a couch. Too big for a chair, though.



There is an amazing thermal sensor available right now which does occupancy exactly the way most people thinking of home automation occupancy wish it would work. It’s almost instantaneous, it can tell when there are two people in a room and one leaves, it even works with HomeKit although uncertified. It’s just very very expensive from a very small company. People who have it seem to love it, but you are talking about a cost of $ 200 per doorway. Maybe $ 120 each if you do at least five rooms. Oh, and it’s plug in, not battery.


It runs locally. I’m not 100% sure, but I think this would continue to work even if the company goes out of business, at least via HomeKit. I would check with them to be sure though.

I can’t afford this myself, but as a wheelchair user it is definitely on my “when I win the lottery“ wish list. The engineering on this thing is amazing.

So those are two “right now” possibilities, depending on the exact use case.

I know lots of people using some variation of a pressure mat, and if you go the DIY route it can be pretty inexpensive. You don’t have to carry anything with you, and it’s able to recognize true occupancy because it’s based on the physical weight of something in the room. A person sitting on a chair or lying on the bed, but maybe even a coffee cup sitting on a particular coaster.

I don’t personally know anyone using the hiome thermal sensor system, but all the hands on reviews have been good. It’s just very expensive.

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