How Do GPS Trackers Work?

GPS, or Global Positioning System, uses satellites to determine the location of a GPS receiver anywhere on Earth. GPS satellites transmit data to a receiver such as your smartphone, a GPS tracker, or a GPS navigation system.

We’ll briefly explain the science behind GPS, how GPS trackers work, and their pros and cons. We’ll also point out the different types of GPS trackers and how to put them to good use.



Stay Safe! Sign up for SafeWise's weekly newsletter.

Get updates on the latest safety news, product releases, and deals.

By signing up, you agree to our Terms and Conditions and Privacy Policy.

What is GPS and how does it work?

The data at the heart of a GPS signal is time—specifically, the exact time the signal left the satellite. The receiver then logs the exact time it gets the signal, and the time difference is computed to a distance.

The receiver’s location can be estimated with 95% accuracy after measuring its distance to at least four satellites.

(If you’re looking for a more technical explanation, we recommend reading The Mathematics of GPS Receivers.)

GPS equivalents around the world

Originally developed for military purposes during the Cold War, the phrase GPS refers only to 31 satellites operated by the US. A few other countries or entities have their own versions of GPS—collectively called Global Navigation Satellite Systems (GNSS).

Russia, China, India, Japan, and the European Union are the only other countries/entities with their own GNSS—undoubtedly because it costs a lot of money to send satellites into space. Each country has its own acronym or nickname for its satellite constellation:1 

  • China: BeiDou (35 satellites, global coverage)
  • EU: Galileo (30 satellites, global coverage)
  • India: NavIC (8 satellites, regional coverage)
  • Japan: QZSS (4 satellites, regional coverage)
  • Russia: GLONASS (24 satellites, global coverage)

You don’t have to stay in the US to use GPS-enabled devices—GPS offers worldwide coverage, as do GLONASS, BeiDou, and Galileo.

But that doesn’t mean every single GPS-enabled device works abroad. If the device uses “assisted GPS” technology, it also uses a SIM card to connect to cellular networks—and those aren’t global.

What is A-GPS?

A screenshot of the Bay Alarm Mobile GPS button's location tracking app.

A device with assisted GPS or A-GPS relies on more than just satellite signals to figure out your coordinates. Cell towers and Wi-Fi networks also send signals to your device that can be used to triangulate your location.

The device then averages the data from all three sources to give a more accurate location analysis.

Why is assisted GPS necessary?

A-GPS is especially helpful when there’s no direct line of sight between your device and the satellites 12,500 miles away. Anything from trees to walls can get in the way of satellite signals and make them less accurate. Wi-Fi and cell signals fill in the gaps.

But relying on Wi-Fi or cellular signals alone also has some disadvantages, especially in terms of infrastructure. Many parts of the US still lack cell towers, and Wi-Fi positioning’s useless if there are no Wi-Fi networks nearby.

Light Bulb
What about Bluetooth tracking?

You can also link two devices via Bluetooth and use one to find the other, but their range is limited to just a few hundred feet. Apple AirTag and Tile Mate are Bluetooth trackers.

How GPS trackers work

You’re probably familiar with using GPS to navigate a strange area, like when Siri tells you how to get to your hotel. But GPS trackers are becoming more and more common for keeping an eye on family members, pets, vehicles, and belongings.

These trackers send signals to a smartphone app or web-based dashboard at specific times. The moment you get those location alerts depends on the device:

  • Predetermined intervals (every minute, every hour, etc.)
  • When requested through the smartphone app
  • When sent by the wearer
  • When crossing a geofence

The tracker’s current location (and, if the device allows it, location history) is then shown on a map within the smartphone application.

What’s a geofence?

A geofence is a virtual fence. The fence’s boundaries are set on the GPS tracker’s smartphone app. When the GPS tracker crosses the geofence, the app sends you a text or push notification.

For example, if your kids wear GPS-enabled smartwatches, you might set up a geofence or “safe zone” around the cul-de-sac where they’re allowed to play. If they start to wander away, you’ll get a notification and can check on the situation.

Screenshots: SafeWise

Geofencing is also used for smart home automations. For example, you might set up a geofence around your home and have your outdoor lights turn on when your GPS-enabled device (a smartphone, in most cases) enters the area.

Types of GPS trackers and their benefits

One of the great things about GPS trackers is they encourage independence in people who might feel vulnerable without a safety net. They also help us find lost items and keep tabs on loved ones without hovering.

Here are some of the main types of GPS trackers and how they’re commonly used:

  • GPS trackers for kids help parents confirm that their kids are where they’re supposed to be, whether it’s school, home, or a friend’s house. The best ones learn your child’s routine and notify you if there’s a sudden change from the norm.
  • GPS trackers for pets keep tabs on your dog or cat’s location, whether they roam freely or are in the habit of running off. The best ones include lights so you can see your pet in the dark.
  • GPS-enabled medical alerts share the wearer’s location with a professional monitoring center when they indicate they need help. Some also allow caregivers to view the wearer’s location on an app.
  • GPS trackers for people with Alzheimer’s or dementia include geofencing so you’ll get an alert if your loved one wanders out the door.
  • Vehicle trackers can help you recover your car if it’s stolen. The best ones plug into the car’s OBD port and have extra features like speed alerts, crash detection, and more.
  • Personal safety apps share your location with friends or 911 dispatchers at the touch of a button. The best ones also discreetly record what’s going on around you.

You can also use GPS trackers to keep tabs on any kind of item you fear might get lost. For example, pop a GPS tracker inside your luggage just in case the airline loses it. These trackers don’t need any extra features—basic GPS functionality will do.

GPS tracker risks and disadvantages

As with all kinds of technology, there are some risks and disadvantages associated with GPS trackers.

1.   You could be tracked without your knowledge

It’s all too easy for someone to place a magnetized GPS tracker under your car or slip a tiny Apple AirTag into your purse with the intention of following you from afar.

And that’s not just a theoretical problem—Apple had to create an alarm system for its AirTags to let people know when these trackers were nearby.2  Then some people learned how to remove those alarms to continue tracking others without their knowledge.3 

While it’s unclear how to combat silent AirTags, we recommend learning what to do if you think you’re being followed.

2. Location data could be viewed or shared

If you aren’t cautious about using strong passwords, two-factor authentication, and private Wi-Fi networks, it’s possible someone could hack into the companion app to view location data.

While this is rare and not unique to GPS tracker apps, it’s a possibility. You can combat it by beefing up your device security:

Make sure you also read the company’s privacy policy before you purchase a device or download an app so you understand how your location data is kept private.

3. You probably have to pay for a subscription

Another downside is that you often have to pay a monthly fee to use GPS tracker apps.

The subscriptions cost around $10 to $40 a month, depending on the company you choose and how many other features are included in the device.

4. GPS trackers aren’t always accurate

Inaccuracy is the biggest risk associated with a GPS tracker. Sometimes it’s obvious that the tracker’s glitching—like when your kid is supposedly 3,000 miles away when you just dropped them off at school.

Other times, a tracker’s inaccuracy could cause some parental panic—like when it shows your child is at the subway station instead of at their friend’s house. Make sure you do some detective work before you believe an odd GPS location.

Here are some common reasons why GPS trackers don’t work:4 

  • The device uses only GPS instead of A-GPS.
  • The device uses A-GPS but there aren’t any cellular towers or Wi-Fi networks nearby.
  • Tall buildings, dense trees, and other obstructions block or reflect the satellite signals.
  • Mapping errors in the app.
  • The device is being used indoors or underground.

Even in the best conditions, GPS readings are typically off by an average of 16 feet.5  

Final Word

We think GPS trackers are worth it despite their disadvantages. Still, it’s smart to not rely on GPS trackers to the point where you take basic safety precautions for granted.

Related articles on SafeWise


Sources

  1. GPS.gov, “Other Global Navigation Satellite Systems,” October 2021. Accessed April 26, 2022.
  2. Alex Kirschner, Apple, “An Update on AirTag and Unwanted Tracking,” February 2022. Accessed April 26, 2022.
  3. Napier Lopez, The Next Web, “PSA: Watch Out for Modded ‘Silent’ AirTags That Make It Harder to Stop Stalkers,” February 2022. Accessed April 26, 2022.
  4. GPS.gov, “GPS Accuracy,” March 2022. Accessed April 26, 2022.
  5. Frank van Diggelen and Per Enge, Institute of Navigation, “The World’s First GPS MOOC and Worldwide Laboratory Using Smartphones,” September 2015. Accessed April 26, 2022.
Cathy Habas
Written by
Cathy Habas
With over seven years of experience as a content writer, Cathy has a knack for untangling complex information. Her natural curiosity and ability to empathize help Cathy offer insightful, friendly advice. She believes in empowering readers who may not feel confident about a purchase, project, or topic. Cathy earned her Bachelor of Arts degree in English from Indiana University Southeast and began her professional writing career immediately after graduation. She has contributed to sites like Safety.com, Reviews.com, Hunker, and Thumbtack. Cathy’s pride and joy is her Appaloosa “Chacos.” She also likes to crochet while watching stand-up comedy specials on Netflix.

Recent Articles

Neighbourhood homes in the United Kingdom
The Best Home Alarm Systems in the UK
Find the right alarm system to protect your UK home. SafeWise recommends security systems for...
safewise's best home security systems
10 Best Home Security Systems of 2022
After hundreds of hours of tests and research, plus a combined 50+ years of experience,...
Abode, Frontpoint, ADT Safestreets logos as alternatives for Vivint
Alternatives to Vivint
Vivint isn’t for everyone. We researched and found three other home security systems to better...
Senior woman hugging dog
The Best Medical Alert Systems of 2022
See which medical alert system is the best to keep you and your loved one...