Once out of the range of a WiFi access point (AP), it becomes much more difficult to transfer data Over-the-Air. Solving this issue often involves having to purchase a more expensive board that features an LTE modem, along with a SIM card and an associated data plan. This adds up quickly due to paying 30 to 50 cents per megabyte. If you just plan on having a few sensors fairly close to a central area, such as an infrared sensor in a backyard birdhouse, then an LTE device would be overkill. Thankfully, Particle has a lineup of mesh devices that are based upon the Threading protocol, which sends data over Bluetooth up to 30 feet away. By taking advantage of mesh networking, your project's cost and complexity can be greatly decreased, while still allowing for great IoT projects to be developed.
As previously stated, Bluetooth mesh is a way to connect devices together via the Bluetooth protocol in order to share data without a centralized, external access point. Rather than having each device connect to a router, they can share a single connection to the "outside world" and simply transfer and route data between themselves.
Particle has an online service that lets users write, compile, and even flash their code all over the air, so remote updates among many fleet devices is now extremely easy. Each board can utilize the builtin mesh functions to publish and/or subscribe to message topics, letting them send data to each other and also the primary access point in order to send it to the Particle Cloud.
Particle has a line of mesh boards that each have the same processor, but differ by supporting different communication protocols, such as WiFi and LTE. The Xenon board is the most basic, and at just $15, it is perfect as a repeater that can relay signals along to other devices, or it can act as an endpoint connected to a sensor or actuator.
The Argon is a Xenon, but with WiFi as well. Argons are used as access points for the other mesh devices, and it connects to a router in order to send and receive data to/from the Particle Cloud.
Finally, the Boron is a mesh device that supports LTE, letting you save money by only needing one cellular data access point without the need for more expensive LTE-enabled devices and SIM cards.
Mesh networks are extremely versatile and can be adapted for use in many applications. They are especially great for outdoor networks where there might not be enough power to run an entire WiFI router. They are also good for when you want many devices in close proximity to all communicate without the need to configure each one individually, thus saving time and complexity. By placing the boards at regular 20-30 foot intervals, you can easily extend your project's reach to well beyond your house or office space.