Smart Door Locks That Support Geofencing And Auto-Unlock

I sometimes wish that I lived in a posh mansion with a dedicated doorman, but failing that a standard doorman would work just fine:

(via GIPHY)

Of course, not all of us have that luxury either! The next best thing is a front door that automatically unlocks itself as you approach it, so that you don’t have to get your keys out.

Smart locks offer auto-unlock as you walk towards your door, using Bluetooth, GPS and something called Geofencing. This is very convenient, but comes with some drawbacks too.

How auto-unlock works

As already touched on, auto-unlock is the ability for a smart door lock to detect that you’re nearby, and unlock the front door as you approach. This means that you don’t need to get your phone out and access the app, or get keys out and get the right key for the lock. It just works – automatically.

This works by firstly downloading your smart lock’s mobile app, and then the app relies on you having a number of technologies enabled on your phone:

  • GPS (also called ‘Location’) – used to determine exactly where you are in your neighborhood, and when you get to within 100-200m (328-565ft) away, the app goes into an increased awareness mode where it’ll be checking more frequently whether you’re coming home and approaching your front door.
  • WiFi – some apps also use your phone’s WiFi to see if you’ve connected to your home’s WiFi. This can help determine whether you’re sat on your driveway, about to enter the house. This can also be used to determine that you’ve just left home (as the WiFi signal will get weaker and weaker rapdily – WiFi range isn’t great.

    August uses WiFi for its auto-unlock functionality, whereas Nuki locks do not.
  • Bluetooth – this is similar to WiFi in that it has a shorter range – sometimes just 10m (33ft), which is the distance that some smart locks will rely on bluetooth for to determine whether to smart lock/unlock. Again this makes sense – if you’ve just pulled into your driveway, Bluetooth’s short range means that your smart lock will quickly be able to determine that you have arrived. It won’t have accidentally picked you up from 400ft away, so a valid Bluetooth connection is a strong sign that you have returned home.
  • Geofences/iBeacons – these are actually two different technologies, but they’re similar enough to be mentioned together (for now). As we’ll see below, geofencing relates to having a virtual square or circle drawn around your house. When you cross over this digital fence, it’s a big sign to the smart lock app that you have left home (or are arriving back home).

What is geofencing, and how does it work?

Geofencing refers to a smart lock app’s ability to detect whether you’re coming home or not, by drawing virtual boundaries around your house and neighboorhood. If you cross one of these boundaries, it triggers a digital proximity alarm – and the app will go into an increased awareness mode.

This mode means that it’ll start checking more frequently to determine whether you’re driving back to your house. When you go very close to the house, it can then unlock your home’s front door lock.

In other words, the smart lock will work with your phone to build up the following sort of picture as to your whereabouts:

A Google Maps diagram with an orange pin showing home (not my actual home!), then two geofences at 10m and 100m points to show the virtual boundaries the lock app works off.
Illustration from Google Maps about how two virtual boundaries – geofences – can be used.

In other words, there are two main geofences in use:

  • A short range geofence at 10m/33ft or 20m/66ft – this can rely on Bluetooth and WiFi connections, in addition to GPS data to ensure that you are very close to your house. If a Bluetooth and WiFi signal is established, you’re likely to be outside your house and so the app will be actively preparing to open your front door when it detects you approach it.
  • A long range geofence at 100m/328ft or 200m/656ft – this will use mobile data and GPS to determine that you might be approaching home (after crossing into the outer geofence) or that you have left the neighborhood and the app can stop checking your whereabouts as often.

Due to a range of power saving options, smartphone apps are unable to check your location every couple of seconds, which is why geofences are used as a sort of heuristic approach to see that you might be returning home. As you get closer, the app can then start checking more frequently.

This clever approach helps preserve your mobile battery (and data allowance), whilst still offering seamless auto-unlock capability.

In terms of how geofencing works, you’ve probably worked out by now that it’s very driven by GPS. After all, knowing where you are in your neighborhood is exactly what GPS is designed to do.

Having said that, Apple phones also offer a feature called iBeacons. This technology allows your phone to interact with markers – beacons – placed around towns and cities that ping to/from your phone, providing an alternative way of determining your location.

Two people standing under lots of bullet CCTV cameras
We don’t know where you are, honest…

This technology was spoken about a lot in 2014 (it was unveiled to developers in 2013), especially since a German restaurant used it to track its customers dining habits – even down to tracking their favorite seats and bathroom usage.

Some shops are also using this to track a customer’s location in the store, and there has been discussion around showing personalized adverts on TV boards based on iBeacons.

This technology hasn’t completely taken off yet (thankfully..?!), but it’s shipped with all modern iPhones and so some smart lock makers are also using iBeacons as another way of determining your location. This is handy if GPS is turned off or being a bit tempremental.

Downsides of auto-unlock and geofencing

Whilst it’s cool to approach your home and have your front door unlock automatically, there are some flaws which I wanted to cover:

  1. Phone features like ‘Power saving mode’ can stop the auto-unlock feature working. This is because such modes can prevent apps from working in the background, such as polling GPS data to determine your whereabouts. However without this information, the smart lock app can’t see if you’re returning home and/or approaching your front door.

    August give tips on improving this feature on Android and iOS, discussing how it can be left to run in the background and not be ‘optimized’ (i.e. restricted) for battery purposes. Nuki suggest similar actions.
  2. You have to leave GPS, internet (WiFi and/or mobile data) and Bluetooth on. Turning all these features off in your smartphone’s menu will stop your smart lock from being able to unlock itself as you approach the door… or more worryingly: it could stop your door from locking itself when you leave home.

    Whilst most people do leave these features on 24/7, I know of a few people (myself included) who turn them off when they don’t need it. I personally hate going to a few shops, and then an hour later having Google Maps ping me and asking me to review the exact shops I visited, and the time I spent in each. It’s creepy.

    Hence unless I’m doing something that requires GPS/mobile data/Bluetooth, I turn them off when I’m out and about. Yes this puts me against the norm and means that smart locks aren’t ideal for me, but I wanted to flag this point up nonetheless.
  3. Unwanted auto-unlocks. The last thing you want is a door that unlocks itself, and whilst current smart door locks are pretty good at working as expected, there have been cases – especially in the early days – where a smart lock will unlock by mistake.

    Or worse than this, there have been cases when a smart lock will invoke auto-lock after someone with the app returns home, but it then stays in ‘active awareness mode’. This increases the chance that it will auto-unlock by mistake, since it’s still actively scanning for reasons to unlock. This has mainly been fixed via software updates (after all, if it’s just auto-unlocked, it’s unlikely that someone else is about to imminently return home), but it does highlight that software issues can cause some worrying consequences.
  4. Smart locks rely on battery power. Consumer smart locks aren’t hardwired. Instead, they rely on batteries to power them. This makes sense because you can’t run wires through your front door to power them, but it does mean that your whole front door lock can fail if the batteries fail (and you ignore the app’s battery warnings!). Having a smart lock with the option of a backup key is therefore quite important – or at least, make sure that you have another way of getting into your house (I mean a backdoor – trying to high jump through your bedroom window may not be practical!).
  5. Price – smart locks need to contain a bunch of cool technology in order to provide auto-unlock (including various communication chips – GPS, bluetooth, internet, etc). However this comes at a price, and the August Smart Lock Pro is currently $200. This is down from $280, but it’s still quite expensive compared to a $20 door handle and key.
  6. May not support your current door – many smart locks require your door to have a single-cylinder deadbolt. This is the most common lock type, especially in newer doors, but not all doors have this. If yours isn’t compatible, having to change your door lock is an added expensive on top of the already-expensive smart door lock.

Smart locks that support auto-unlock with geofencing

There are quite a lot of smart lock options out there, and nearly all support auto-unlock (employing geofencing for accuracy and speed). My favourites, however, include:

  • The August Smart Lock Pro, which is currently just $193.96 on Amazon (down from $280). This is considered one of the best smart locks on the market, with 4.3/5 stars and offering ‘door sense’ – a way of notifying you if your front door is securely closed or not.
  • The cheaper August Smart Lock is $148 (down from $200) and also has 4.3/5 stars. The Pro version comes with more integration options, offering Zwave, HomeKit and Alexa capability out the box – unlike this cheaper option which does not. What this practically means is that if you purely want a smart door lock and to control it with the phone app, this cheaper version will be fine. But if you have lots of smart home tech and a smart home hub, the Pro will offer you more integrated options.
  • COLZER offer a more budget option at $99, although its 4.4/5 rating and auto-unlock capability shows that it’s not a cheap option: it still does what most customers want it to do.
  • The Yale Assure Lock SL isn’t cheap at $223 (down from $299), but it has a 4.2/5 rating and it offers a nice, sleek touchscreen keypad as a fallback option if you don’t have your phone on you. It also works with the August app (Yale purchased August in 2017).
  • The Nuki Smart Lock 2.0 isn’t as well rated at 3.9/5 and it’s currently unavailable to buy on Amazon, but it’s well regarded elsewhere and its auto-unlock capability (along with iBeacon-driven geofencing) is known to work well overall.
About Tristan Perry

Tristan Perry is a software developer who is passionate about tech gadgets, DIY and housing. He has therefore loved seeing smart homes hit the mainstream. Tristan also has an academic background (in Math & Computer Science), and so he enjoys digging into the technical ways that smart home devices work.

Tristan owns close to a dozen Amazon Echo devices, way too many Philips Hue bulbs and lightstrips, a boat-load of Ring Cameras and Doorbells... and a bunch of other smart home devices too (from Reolink, Google Nest, GLEDOPTO and others).

If you have any questions, feedback or suggestions about this article, please leave a comment below. Please note that all comments go into a moderation queue (to prevent blog spam). Your comment will be manually reviewed and approved by Tristan in less than a week. Thanks!

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