NEARLY PERFECT Battery Power Presence Sensor – LinknLink eMotion Air Review

This is the LinknLink eMotion Air, the first battery powered mmWave presence sensor, and it’s SO NEARLY PERFECT. When LinknLink offered to send one over – no strings attached, they have no editorial control nor see this video before it goes live – I jumped at the chance to test it out. I’ve been searching for a good presence detection solution for my house. Even though I now own the place and can run wires and cables in the walls and whatnot, for a little presence sensor like this I really don’t want to. I don’t want to take up a plug socket with another USB charger just to power a little sensor. Plus, I really wanted millimetre wave. The Sonoff one I bought and reviewed a while ago now is 2.4GHz, which does work fine enough, but mmWave should offer much more sensitivity which is crucial for actually good presence sensing, and in theory that’s what this offers, so let’s take a look at it, get it set up, then see how it performs.

First though a very brief explainer on why presence sensing is important in a smart home. The ability from your smart home system, in my case that’s Home Assistant, to know that you are in any given room opens up a bunch of possibilities, including smart heating that follows you around the house, lights auto turning on and off depending on room occupancy, and even essentially a DIY home security system. All really cool features. The problem is most ‘motion sensors’ are PIRs – passive infrared sensors – that require a decent amount of movement AND often have a noticeably slow response time/latency, and because of that aren’t good for knowing if you’re still in a given room but just, like, sat on the sofa. I’m sure you’ve had it where the public bathroom light turns off because you’re in the stall and haven’t moved for a minute, then have to wave your arms hoping the light turns back on. That’s a PIR motion sensor. Presence sensors use radio waves to detect motion and can be so sensitive that they can detect your chest rising and falling from breathing, which means it’s much better at tracking the fact that someone is still in a given space. That is, in theory, what this thing offers, but this just uses AAA batteries, which is a first.

Getting the eMotion Air, I’m just gonna call it the Air from now on because eMotion is killing me, is a palm-sized square puck with a mounting bracket clipped on at the back, and a bit of a two-step design. The mounting bracket has two decently strong magnets embedded so you can stick it straight to something metal, or you can screw or stick it. Dealer’s choice really. Under that is the battery cover where you’ll fit the three AAA batteries, and at least visually that seems like that’s it. Except you’ll quickly realise that the front plate moves – and clicks! That’s because the front plate is actually a switch too, and that little hole? That’s the built in light sensor. There’s also a temperature and humidity sensor in there somewhere too. So not only is this a battery powered mmWave presence sensor, but it’s also a light, temperature and humidity sensor, and a smart button. Sweet! Oh, and this all works over either Bluetooth or Zigbee, and is even part of the “Works With Home Assistant” class which is amazing.

What isn’t so amazing is the Air’s setup process. While this is a Zigbee device which can connect directly to Home Assistant over ZHA or Z2M, the manual and the website both make it clear you MUST use their app to set it up first. This is somewhat sacrilege to me, especially because they REQUIRE you to create an account just to use their damn app. I hate this with a passion. Stop this BS data collection LinknLink. I’ve already bought your product, you don’t need my soul too. Anyway, inside the app you get the basic info, although if you want to change any settings you actually have to hold the button down for 10 seconds to put it into a config mode, then you can change what light level corresponds to “normal” “low” and “high”, what sensitivity the motion sensor is set to and stuff like that. If you want to then connect it to Home Assistant via Zigbee you’ll need to hold the button down for 15 seconds to put it in Zigbee pairing mode, although it’s worth noting that I had a bit of a hard time actually getting this connected. It took a while to be discovered and start the interview, then it just… didn’t pair. I tried it a few times, eventually just leaving it and occasionally pressing the button to keep the board awake, and it finally paired properly. 

Once paired you get the five sensor entities – motion, humidity, light, button and temperature, plus the battery level (the firmware is listed as “unknown”) – although immediately I found some quirks. When using their app via Bluetooth the button can report all the usual states – single, double and long presses – but via Zigbee all you get is a toggled state – so pressing the button for the first time reports as ‘closed’, but pressing it again toggles it back to ‘open’. That means you need your automations to rely on the change, not the actual state value, which sucks because if the device drops off the network or the network restarts the automations will fire because going from “unknown” to “open” is a valid state change, unless you are really careful setting them up. Also you just get less functionality over Zigbee. Only single presses, no double or long press values. That’s a shame. There’s also the temperature sensor which seems to read slightly higher than my other sensors in the same room, albeit not right next to each other.

But there’s also the main show, the motion sensor. That’s an interesting one, because while this is a mmWave sensor using 24GHz radio waves to detect motion, it isn’t quite as sensitive as Aqara’s FP2 60GHz sensor. It is much faster to respond than a PIR sensor, and is a lot more sensitive, but it isn’t perfect. The app has this at a hold time of three minutes by default – meaning it continues reporting motion for at least three minutes after it has last registered motion, but at least in my testing so far that isn’t enough to truly do presence detection. We’ve been sat in the living room and it reported clear, despite two people sat across from it. The Aqara one is meant to be sensitive enough to track your breathing, but this doesn’t seem to manage that. In fact, I’ve been writing this script on my laptop in the living room directly across from it. I’m typing away on my keyboard, but as you can see from the screen recording, it just reported the room is clear – not occupied. I’m here! It took me raising my phone to record both my screen and the sensor for it to re-trigger, and if I keep sitting here typing away but not making any big movements it’s going to report clear again in a couple minutes. This is also set on high sensitivity, so as far as I can tell this is about as good as it gets. Technically this does have a self-learning option (that is enabled) to basically learn the room to get more accurate at detecting presence, but it’s been a couple days with the sensor in my living room and I haven’t seen a noticeable improvement in its sensitivity and accuracy. I think you’d absolutely want to set this to have a longer hold time for better accuracy, and it is a shame it isn’t properly sensitive enough to detect even two people sat in the room. Even more strangely, it seems there’s also a delay between clearing and re-detecting. I was sat waving my arms around and it took a good 30 seconds of movement before it detected me. Weird!

The fact that this is battery powered, comes with a proper light sensor, a decent enough temperature sensor and acts as a smart button, oh and is like £20, and works over Zigbee makes this a pretty solid recommendation from me though. While it isn’t perfect, it’s just too good to not want this in your smart home. The light sensor is something I absolutely need in a presence sensor to be able to know if presence means lights should be turned on or not. The temperature readings are also useful from a data and HVAC perspective, and the ability to use this as a smart button – it even comes with a handful of stickers to show what it does – is pretty great. Really useful. For the price, and the functionality, I’d be more than happy to have these at home. I am still keen to try out the wall-powered Aqara 60GHz sensors which offer things like multiple zones, multi person detection and even more sensitivity, but this is impressive in a lot of ways. The whole requiring an account to set the damn thing up is a hard no though. I’m absolutely deleting the account and app after I’m done filming.