The Beginner's Guide to Geofencing
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The Beginner’s Guide to Geofencing

We’re going to cover everything you need to know about geofencing. Whether you want to use geofencing to protect your property, keep your loved ones safe, or send location-based communications for your business, we’ve got you covered.

By the time we’re finished, you’ll have a clear understanding of:

  • What geofencing is
  • How geofencing works
  • What geofencing is used for
  • How reliable geofencing is
  • How to set up geofencing

Let’s start by taking a closer look at what geofencing actually is.

What is geofencing?

Geofencing is a virtual perimeter around a geographic location. An app or software uses the Global Positioning System (GPS) to define the “fence” and track if a device enters or exits the area. In SpyTec GPS, we call geofences “boundaries,” because when you create one with a GPS tracker, you’re establishing an area you want the tracker (and the item, pet, or person it’s on) to stay within. 

Depending on what a geofence is being used for, it may monitor a specific GPS tracker, any mobile device with a corresponding app, or a wider range of GPS enabled devices (personal computers, smartphones, and tablets). If the tracked device crosses the geofence, it triggers a notification—a text message, push notification, or email—that either goes to the device itself or a separate device monitoring the geofence.

How does geofencing work?

Since geofencing uses GPS to define its virtual boundary, if you want to understand how geofencing works, you need to start by learning how GPS works. 

How does GPS know a device’s location?

The Global Positioning System (GPS) is a network of more than 30 satellites that orbit the Earth, constantly transmitting their coordinates and the time. A GPS receiver (such as your smartphone or a GPS tracker) can pick up these satellite signals, and anytime a receiver picks up signals from four or more satellites, GPS does a little geometry to estimate the receiver’s coordinates.

Basically, it knows how fast the GPS signal travels, and it knows the locations of the four (or more) satellites that sent them and the time they transmitted, so it calculates the speed over time to determine how far the receiver is from each satellite. If there are at least four satellites, then the GPS can give a pretty reliable estimate of the receiver’s location at the moment it picks up the signals.

[Image of a GPS tracker in SpyTec’s platform]

So that’s how the GPS knows a device’s location.

How does GPS know when a device crosses a geofence?

While you might be trying to create a geofence around your home, your business, or another physical location, what you’re actually doing is establishing your virtual barrier’s coordinates (longitude and latitude). These coordinates are almost always overlayed with a map, so you can easily set your geofence around a building or property, but the coordinates are what the geofence is really monitoring. When a device’s coordinates cross over the geofence’s coordinates, it triggers a notification.


[Image illustrating a geofence being triggered. Could be in the software or just a graphic.]

How does a geofence send notifications?

There are several ways a geofence may send notifications, depending on what kind of notifications it’s sending. Push notifications use cellular data networks or Wifi. Text messages use radio frequencies. Emails use Wifi or cellular data. When a device crosses the geofence, your app or software detects it using GPS signals, then transmits the notification—either to you, an email address, or the device that crossed the geofence.

So if your geofence is set up in the middle of nowhere and there’s no service, a mobile device won’t receive the notification until it gets reception.

What is geofencing used for?

Geofencing has a wide range of applications including security, fleet management, and marketing. Here are a few different ways people and businesses use it.

Protecting property

A geofence won’t necessarily stop someone from stealing your car or walking off your campus with expensive company property. But it will let you know the moment that happens. One of the most common ways consumers and businesses alike use geofencing is to monitor vehicles and other valuables. This only works if you have a GPS tracker installed on the object you want to keep within the geofence. When the tracker leaves the geofenced area, it sends a notification to your device.

Note: If you’re using geofencing to protect your property, you’ll want to make sure you choose a small, easily concealable GPS tracker (like our GL300MA model). You wouldn’t want a thief to spot your tracker and disable it, throw it away, or attach it to something else!

Targeted advertising

Digital advertisers are always trying to make their ads more relevant—because that makes them more effective. You can use geofencing to target your ads to people in specific locations. Your geofence might encompass an entire city or zipcode. Or it might home in on a small radius around your company campus, a competitor’s campus, or another location that’s relevant to your ad.

You might, for example, want to target people who are leaving a competitor’s campus. Or people within walking distance of your store. Or people who are attending a conference, concert, or another event.

(In marketing, this is sometimes referred to as geotargeting, but it relies on geofences.)

When someone crosses the geofenced area, they become eligible to see your ad on whatever platform you’re using (Google Adwords, Facebook, etc.). Depending on the advertising platform, you can also combine geotargeting with other demographic data like age, sex, or language.

Location-based push notifications

Push notifications use geofencing in a similar way, but they work a little differently. You can only send someone a location-based push notification if they have your app on their mobile device, and their mobile device crosses your geofence. You might use these to tell people when there’s something you want them to see, an offer they can take advantage of in-store, or to drive them to take an action in your app.

Alternatively, some lifestyle and productivity apps allow people to set their own geofences around specific locations to remind them to do something whenever they’re in that area.

Monitoring loved ones

In some instances, it’s a major safety issue if someone leaves a designated area, such as a home or care facility. Some people may use geofences and GPS trackers to ensure their kids or loved ones with dementia stay where they’re supposed to be. Of course, this requires a portable GPS tracker. (This could be a smartphone or a dedicated GPS tracker.) When the GPS tracker leaves the designated area, it alerts the guardian, who can either track the person down or notify the police.

Automating time cards

Some companies use geofences to automatically “punch in” and “punch out” employee time cards. If someone’s job requires them to be in a specific geographic area (such as the company campus or a specific facility) and they can’t do their job outside of that area, this can be a way to ensure they don’t have to worry about clocking in or out, and you don’t have to worry about anyone leaving early or arriving late.

Emergency alerts

Geofencing has some invaluable applications for public safety. When there’s a tornado or hurricane coming your way, a kidnapping nearby, or another regional emergency, local government agencies may use geofencing to send an emergency alert. These may tell people to evacuate an area, take extra precautions, or be on the lookout for a particular vehicle or person.

How reliable is geofencing?

GPS is remarkably accurate. But it’s not perfect. Anytime you use GPS to determine your location, it’s important to remember that it’s an estimate. The latest performance data the US government has released claims GPS can determine your location within 4 meters, and that it’s 95 percent accurate within 7.8 meters.


This means when your GPS says you’re in one place, you might really be 10 feet further north. Or southwest. Your GPS is really saying, “I’m almost positive you’re within about a 25 foot diameter of this spot.”


When there’s a difference between your actual geographic location and the location your GPS says, this is referred to as “GPS drift.” It’s probably not going to cause problems for your Google Maps route (unless your GPS thinks you’re on a different road). But it’s important to keep in mind how that could affect your geofence.


The smaller your geofence is—or the closer a tracking device is to the edge of your fence—the greater the risk that drift could incorrectly trigger (or fail to trigger) a notification. That’s probably not a big deal for your targeted advertising campaign or marketing-related push notifications (you might miss or gain a person here or there), but if you’re trying to track property or people, it might cause some problems now and then.


Thankfully, there’s a pretty simple solution. If something or someone isn’t supposed to leave an area, make sure the radius of your geofence is at least 26 feet wider than it needs to be. Then you won’t have to worry about getting a “false positive” when your tracker gets near your boundary. If you get a notification when your boundary is bigger than it needs to be, you can be confident that it’s because your tracker isn’t where it’s supposed to be.


There’s one other thing you may need to consider about how reliable your geofence is. Since four GPS satellites have to have line of site on your GPS receiver in order to estimate its location, it’s important to be aware of factors that can inhibit GPS satellite signals. 


Mountains, buildings with thick walls, and sometimes even trees can delay or reflect GPS signals. In most cases, this shouldn’t interfere with your geofence—but you should probably plan for your boundary to at least encompass your entire building, rather than specific areas within a building. For example, a geofence will work great for your apartment complex, but not so great for your individual unit. For businesses, your geofence should probably include your entire campus, your property, or the mall your store is within, not just your warehouse, your store, etc.

How do you set up geofencing?

Setting up a geofence works a little differently depending on the app or software you’re using to set it up. But it will most likely work one of two ways:

  1. You choose a predefined range around a specific geographic location
  2. You drag and drop your geofence on a map

Depending on the platform you’re using, you might start by choosing a city, entering specific GPS coordinates, or placing a pin on a map, and then select the radius you’d like to use. 


With SpyTec GPS, setting a geofence is as easy as clicking on a map and dragging your mouse until you have the boundary you want. Your geofence can be as wide as [insert max perimeter] or as narrow as [insert minimum recommended feet]. (Just keep in mind that GPS locations are estimates within 7.8 meters, or about 25.59 feet.)

[Image (ideally a GIF) showing how to set a geofence in SpyTec GPS]

Want to protect your property with geofencing?

At SpyTec GPS, we’ve built a suite of GPS trackers and GPS tracker accessories for people and organizations to secure their vehicles and valuables. Our intuitive GPS software makes it simple to set a geofence, and our team is always available for 24/7 support.

Check out our GPS trackers, and protect the things that matter.