When building apps using ArcGIS AppStudio, you can integrate external hardware with your app. However, it can be difficult to communicate with the hardware, and to know what to do with the information that you can get from (or send to) it. This overview of Bluetooth, Bluetooth LE, and beacons may help you decide which of these hardware options could be suited to solve your specific hardware communication requirements.
Bluetooth 
AppStudio 3.0 introduced support for traditional Bluetooth connectivity. The most common use of Bluetooth among AppStudio apps has been to connect high-accuracy GNSS receivers to devices. You can also communicate with other sensors using Bluetooth, such as laser rangefinders and environmental sensors. The GNSS Info sample in AppStudio demonstrates how you can connect to a device with Bluetooth. To learn more about using high-accuracy receivers with Bluetooth, see Prepare for high-accuracy data collection.
Bluetooth LE 
AppStudio 3.1 added support for Bluetooth Low Energy (LE). A subset of Bluetooth, Bluetooth LE uses less power and is ideal for more frequent transmission of smaller amounts of data. Code samples for communicating with Bluetooth LE devices can be difficult to offer, as the devices typically transmit data via Bluetooth with proprietary information. The most prolific Bluetooth LE devices in the community are fitness devices. To use your Garmin or Fitbit device, you will need to connect to a proprietary app to see the information: for example, steps, distance, and calories burned. You will be able to use the AppStudio Bluetooth LE components to detect Bluetooth LE devices, but typically you will not be able to interpret the data that is transmitted.
Services, characteristics, and descriptors are how devices package information that they will share via Bluetooth LE. For more information, including a diagram of how services, characteristics and descriptors are related, and sample code, see the BluetoothLEDevice page in the API Reference.
Beacons 
AppStudio 3.2 added support for beacons. Beacons can be considered a subset of Bluetooth LE devices, as they use the same LE protocol, but they make identifier information more readily available, making them suitable for creating alerts and triggers when interacting with them.
When reading about beacons, you will see two terms: iBeacon and Eddystone. In short, these are the Apple (iBeacon) and Google (Eddystone) beacon communication standards, but they do not limit which device you use to communicate with the beacon.
Bluetooth beacons frequently use regions to group beacons transmitting similar or related data together. In Bluetooth terminology, a region is a collective term for a group of Bluetooth beacons with specific shared identifying information; a beacon's region is unrelated to its range or its geographic location.
Beacons can be useful for specific use cases but can be difficult to conceive at first. The most common beacon use case is that of an interactive shop or gallery. When entering a museum, you may be directed to open the museum's tour guide app. In the foyer area, the app shows you general info about the museum. As you enter a gallery space, you are shown information about the room and the collection you are about to see. As you approach an individual exhibit, you are shown information about that specific exhibit. This guided navigation can be achieved using beacons located near each object or entrance to a space. This is an effective way to keep propriety information on site. The user can only see or interact with information while at your venue. Retailers also use a similar pattern to engage with customers: as they approach an item or location in the store, targeted advertising or specials can be shared with them.