Find me some beautiful sensors!

In this article, our guest writer Paul Ockenden is going to compare some Z-Wave door and window sensors - but from a slightly unusual angle!

Over to Paul then, where it all started when someone asked him ....

“Why do so many of the Home Automation devices on the market just look like horrible unattractive boxes? What’s the point of eliminating wires if you’re just going to replace them with something equally as ugly?

Some kit looks so awful only a mother would love its looks! Where’s the design? Please can you recommend some home automation kit that actually looks nice (or even better, is invisible)?

In particular, door and window sensors that don’t look like you’ve glued an old matchbox to the frame.”

That’s quite a brutal assessment of the Home Automation marketplace, but I think the person has a point – many of the devices on offer are just plain ugly! In this Internet of Things (IoT) age we seem to have simply swapped unsightly wires for unsightly boxes.

In order to try to find an answer to this dilemma I had a chat with the lovely and always helpful people at Vesternet, and asked them to send me a few sensors to have a play with, with the proviso that they needed to be pleasing to the eye. A few days later Postman Pat turned up with a package of goodies.

Incidentally, this isn’t just something I’m able to do because I can pull strings as a tech journalist. Vesternet’s enlightened returns policy (14 days for opened but otherwise ‘as new’ products, or a staggering 365 days if the product remains unopened) means that anyone can order several bits of kit and then decide at their leisure and in their own home which bits they want to keep. Try sending stuff back to other shops a year later for credit and see how you get on!

A face for Radio!

Anyway, the first device out of the box is one that split opinions here on whether it meets the ‘pleasing to the eye’ requirement, but it’s still an interesting product. The device is the Fibaro FGK-10x. It’s a conventional two box door or window sensor, where one very small box contains a magnet, the other larger box contains the battery, wireless electronics, and a way to detect the magnet.

There are three common methods for doing the latter – manufacturers can use a ‘reed switch’, a ‘Hall effect’ sensor or an ‘anisotropic magnetoresistive’ sensor.

A reed switch is essentially two skinny bits of metal in a tiny glass tube and under normal circumstances there’s a small air-gap between the contacts, but when the switch enters a magnetic field the two contacts come together and so a circuit is made. It’s a simple idea (invented in the 1930s) but it works well.

A Hall effect sensor, on the other hand, is a solid state device where a signal is generated by the magnetic field density around it and an anisotropic magnetoresistive (AMR) sensor is a device where the resistance is changed by the magnetic field – much as the name implies. Hall and AMR based sensors can be more sensitive, but require additional supporting electronics.   Sounds complicated, but if your tablet or phone is one that goes to sleep when a flip cover is shut it probably uses magnets in the flap and Hall effect or AMR sensors in the device body to sense when to switch off.  So you've probably been using those sensor types without even realising it!

It’s pretty simple to tell whether a sensor uses a reed switch or not – you simply listen to it. With a reed switch based device you’ll hear a quiet but perceptible ‘click’ as you bring the magnet close to the main body. And it’s by doing this that I’m able to tell you that the FGK-10x – like most door and window sensors – does indeed use a reed switch.

So far it all sounds a bit conventional, but there are a few reasons why this particular device is interesting. For starters it doesn’t quite have the ‘ugly box’ form factor of many of its competitors. The main unit is index finger sized, and rounded rather than square, which makes it look quite sleek looking.  The magnet is tiny too, compared to some devices where the magnet is the same size as the Fibaro main body!

Interestingly, this sensor comes in a range of colours which further help with the aesthetics. If you have a dark brown door frame then a normal white sensor will stick out like a sore thumb, but with the FGK-10x you can just order one in dark brown. In fact the "x" in the product code isn’t really an "x" at all (although this is how the device is usually referred to) - it’s replaced with a number. FGK-101 is white, 102 is grey, 103 black, etc. A dark brown one would be FGK-107.

The other reason why the device is interesting is that it has additional inputs. There’s a binary input which you can connect to a volt-free contact such as a push button. Note though that this input is wired in parallel with the internal reed switch, so isn’t really suitable for use as say a door open contact and external doorbell push at the same time. Talking of which, you can see how one of these can be used with a doorbell push in a recent blog article.

More usefully, there’s also a temperature input – you simply need to connect a DS18B20 (a three-pin device that looks a bit like a transistor). These are readily available and very cheap – so cheap in fact that it’s a pity Fibaro didn’t just include one in the design!

Battery life should be over a year in most situations, which is good because it takes a not-that-easy-to-find ER14250 battery – half the size of an AA, but pumping out 3.6V.  I should also add that the version that I reviewed was the older Z-Wave version and subsequently Fibaro have released a new version based on the newer 5th generation Z-Wave chipset, usually either referred to as Gen5 or Z-Wave Plus, depending on the manufacturer.  Other than the change in chipset though I believe that the devices are pretty much identical.

In summary then, the FGK-10x is an interesting device, and certainly different from most other door sensors, but for some people it still might fail the ‘ugly box’ test, so let’s move on.

Paint your own

Next out of the box of goodies from Vesternet is the Door/Window Sensor 6 from Aeon Labs’ Aeotech range. This one certainly isn’t an ugly square box – it’s triangular! Imagine a pub beer mat folded in half across the corners and that’ll give you a rough idea of the size. It’s only 9mm thick, so much thinner than traditional sensors.

The triangular form factor means that it can fit very discretely into the corner of a door or window – you’ll hardly notice it’s there. And the supplied magnets are incredibly small too – Aeon Labs describes them as ‘shards’ – a good name as they are barely 2mm thick.

The obvious difference between the Door/Window Sensor 6 and a more traditional sensor such as the Fibraro that I wrote about further up, is that normally you’d attach the sensor to the frame and the activating magnet to the door or window, but with this device it’s the other way around. This obviously mean that the sensor needs to be more robust, as it’ll get quite a bang when a door slams, but it seems to be up to the job, and the extremely light weight helps in this respect.

Unlike the Fibaro it doesn’t come in a range of colours – only white. But with this sensor the case is made from a special matt plastic that’s designed to be painted, so when you do that it becomes pretty much invisible. It’s such a simple idea, it makes you wonder why other sensors are made from that type of shiny plastic that’s almost impossible to paint, and where if you do manage to get paint to stick to it, the paint then flakes off with the slightest knock!

Another point of departure from the FGK-10x is that the Aeon Labs Door/Window Sensor 6 uses the newer Gen5 chipset . The major benefits of this are increased range and better battery life, although increased bandwidth and better noise immunity are important too. Most of the sensor manufacturers are slowly updating their product lines to include Gen5 capabilities.

Unlike more ‘traditional’ sensors which just have a single point of activation, with the Door/Window Sensor 6 there are magnetic detectors (reed switches – you can hear the faint click) on both shorter sides of the right-angle triangle. This means there’s a lot of flexibility when it comes to mounting the device.

One really interesting aspect of this little triangular sensor, and it’s one that you don’t see very often in this type of kit, is that it uses a rechargeable battery. In normal use you should get between 10 months and a year from the sensor, but when your home automation system starts to show you battery warnings you simply unclip the sensor from the door or window, and recharge it using a standard Micro USB phone charger. It even comes with a Micro USB cable in the box!

A full charge takes a few hours, so obviously you need to arrange to do this at a time when the sensor isn’t needed for security reasons. The lack of removable battery is partly what helps with the robustness that I wrote about earlier – give most battery powered devices a knock and it’s usually the battery that goes flying.

I’m really impressed with this latest Aeon Labs sensor. It’s certainly not one of the usual bland ugly boxes that pervade Home Automation and I for one would be happy to have these blending into the background in my own home.

Through the door

But we’re not finished yet, next out is another device from Aeon Labs, but this one is completely different. Known as the Recessed Door Sensor it actually sits inside the door itself.

Size wise, if you picture a lipstick you’ll be about right. So what you have to do is bore a 19mm hole into the edge of your door, to a depth of 65mm, and a matching hole in the frame, 15mm deep, to hold the magnet. Then, when the door is closed the sensor is completely invisible!

Sounds perfect, doesn’t it? Well maybe. There are a few important gotchas with this sensor. Firstly, it only works in doors, not windows, due to the depth of the hole needed. I guess the clue is in the product name: Recessed Door Sensor. Secondly, it’s only really suitable for wooden doors. It might also fit some uPVC doors but many don’t have the required depth, and with those that do the sensor wouldn’t be held securely because it would be sitting in a void. Drilling into a uPVC door can also damage the seals and drainage channels built into the structure. I really would stick to wooden doors with this sensor.

I also don’t think it feels as robust as the other sensors here. In particular, to change the battery you need to pull a PCB from the main body of the device, but it’s a tight fit (especially once the sensor is wedged into its hole in the door), and there’s nothing to easily grab hold of. The temptation is to take a pair of pliers to the circuit board, but if you look closely it has components right up to the edge.

A simple design tweak could have solved this, but without that my advice is to loop some thin string around the underside of the board before inserting it. That way you can just pull the cord to remove the innards from the tube next time you need to change the battery.  Alternatively you could slightly over-drill the hole to 20mm which should give enough clearance to remove the whole device - it's much easier to take it apart when it's on a flat surface in front of you!

Incidentally the battery might at first sight look the same as the ER14250 in the Fibaro, but in this case it’s a CR2 – they are slightly different in size, and the CR2 is much more commonly available due to its use in many photographic products. The battery should be good for around a year. It’s a Gen5 Z-Wave product, which helps with that battery life and also the RF range.

To be fair, although I’ve criticised the fiddly construction of the sensor this doesn’t affect the day to day operation. Once fitted it works really well, and like I said above, with the door closed it’s totally invisible.

Strip joint

Finally we come to the last item in the box – a Sensative Strip. A slightly strange name, sounding like some sort of bathroom accessory perhaps, but at least it’s easier to remember than an obscure model number. The device doesn’t come from one of the existing home automation manufacturers – it started life as a crowdfunded product on Indiegogo.

There are a number of things that set the Sensative Strip apart from the others here, and the first is the form factor. I think it looks like an emery board (nail file), my wife suggested a long lolly stick. It’s under 3mm thick, and designed to fit into the gap between a door or window and the frame. In practice, most doors and windows (especially double glazed units) will have sufficient space. If for some reason the strip doesn’t fit you can still mount it externally, like a traditional sensor, and because of the slim profile it’s almost invisible – especially if mounted above a door rather than to the side.

Unlike the other sensors here there’s no reed switch. The Sensative Strip uses an AMR sensor. In fact it uses two of them, but more on that in a moment. And also, uniquely among this group the battery isn’t replaceable or rechargeable. It’s built in, and the manufacturers reckon it’s good for around ten years of use.  Obviously it's difficult to substantiate that because it will depend on how often the device is used, so it's something to bare in mind because once the battery expires the device becomes disposable!

It goes without saying that a device as innovative as this uses Gen5 Z-Wave. It’s waterproof too – that’s important if you use it on windows that might be left open when it rains.

I mentioned that the device has two AMR sensors. One is used for the main open/closed detection, the other for programming the device. Where with the other sensors here you have to press a button to put them into pairing mode, with the Sensative Strip you pass a secondary small magnet (which is supplied) over a control zone on one end of the strip. If I was to be picky, such fiddly programming is probably the weak spot of this device, but it’s hard to be critical when a device is as brilliant – and indeed as different – as this one.

Conclusion

Of all of these sensors I suspect the Sensative Strip will be the one that’s most pleasing to someone who finds most home automation kit aesthetically limiting, and who desires non-intrusive sensors and devices.

It’s been great fun testing all of these sensors, and thanks again to Vesternet for all their help!