Cell companies, like AT&T and Verizon, charge tracking companies, like Ping, to use their cell towers to send location information to the customer, so the tracking companies need to charge their customers (i.e. you) to cover this cost.
Tracking/locating devices need a way to communicate their location back to your phone. The three main ways this location information is transmitted are Bluetooth, WiFi and cellular.
- Bluetooth. Ping Home is an example of a device that communicates over Bluetooth. Tile, a competitor, is another. Bluetooth has an effective range between 35 feet to 100 feet from your phone. If you move past that range, the connection to a Bluetooth device disconnects. This makes Bluetooth devices, like Ping Home, great for things like keys and purses - things you lose in your home or office nearby. Since most phones have Bluetooth build-in and the Bluetooth locators obviously have it as well, you don't need to pay extra for it to transfer information back and forth.
- WiFi. Wifi is what you probably have in your house to transmit the Internet wirelessly to your TVs and computers. It's also a communication system, but as you probably already know, it has limited range as well, typically a few hundred feet. Also, most WiFi networks are secure, so if you had a WiFi device lost somewhere, even if it was near someone else's WiFi, if it doesn't have the password it can't send any info. Most devices, even if they have WiFi, don't use it to send information.
- Cellular. Ping GPS and your cell phone are both examples of devices that communicate over cellular. Like your cell phone, Ping GPS and other cellular-based tracking devices need to connect to a local cell tower to send and receive information to a "server." This server can then send that information back down to your phone. In the case of Ping GPS, once the device gets a lock on its location, it tries to connect to a local cell tower to send that information to our server, which then pushes it down to our app. Cellular doesn't require a connection to your phone, like Bluetooth does, and can be accessed anywhere in the world that the right cell tower is present. As anyone with a cell phone knows, the cell companies that provide these towers charge for using these towers to communicate. As a result, any device that is using cellular to communicate needs to pay for the ability to send its location. The companies that make these devices, like Ping, need to charge its customers a monthly fee to cover the monthly fee they need to pay to AT&T, Verizon and other cell companies to use their towers.
So, put simply:
Bluetooth and WiFi are free but have limited range of no more than a couple hundred feet. Cellular can be used anywhere a cell tower is reachable but tracking / locating companies get charged to use these towers and thus need to charge their customers to cover the costs.