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What is geofencing and location detection?

Q: My thermostat knows when I’m close to home and my car automatically locks when I leave. How does it all work and is it a privacy risk?

Lewis Geyer / Personal Photographer

David Taylor

A: You’re actually talking about two very different technologies. Let’s talk about the simplest first: your car works with what’s called radio frequency identification (RFID). The key emits a very low power encrypted radio signal and the car receives this signal and compares it with the “paired” key. If they match, your car will unlock, start, open the trunk, etc.

You can experiment with this by wrapping your key in a few layers of aluminum foil and note how it blocks the signal, thus rendering your key useless. Unbox it and you’re good to go.

Your smart thermostat, by comparison, uses a much more complicated system because it works with your smartphone. Every minute of the day, your phone simultaneously pinpoints its exact location – open a mapping app, it always knows where you are! – and report your location to the cellular network so that text messages and calls can be properly routed to your device.

A smart thermostat like the Nest is connected to the internet through your home Wi-Fi connection. It connects to the online Nest software system, which is also paired with your smartphone. As you move, your phone’s location is reported to the cellular network, which then shares it with Nest software.

Somewhat indirectly, this means that your thermostat and your smarthome know where you are at all times.

So what is Geofencing?

Now imagine setting your thermostat to switch from “Away” mode to “Home” mode whenever you are within a mile of your home. As you ride, it goes into “away” mode, turns off your lights, and adjusts your heating and cooling threshold temperatures to reduce your energy consumption.

The distance from your identified location – your house, in this example – can be thought of as an invisible or virtual fence. A geofence. A… geographical barrier.

It turns out that geofencing can be used in a wide variety of applications. For example, it could notify you when your children leave campus during the school day (cell phone companies offer this service). Advertisements may appear on your phone when you are near their workplace. Imagine a beer promotion the next time you walk into Coors Field!

Finally, there are some privacy implications, but they have more to do with keeping your smart devices online than any geofencing app. Want to keep your location private? You’ll have to turn off your damn phone, but then you’ll be offline. As with so many things with tech privacy, it’s a trade-off.

Dave Taylor has been involved in the online world since the early days of the Internet. He leads the popular technical help site. You can also find his gadget reviews on youtube and chat with him on Twitter as @DaveTaylor.