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There is a lot of confusion regarding the restrictions that are applied by the iOS on apps that want to scan BLE beacons\peripherals. After reading several blogs and Stack Overflow answers, I want to see if I understand all the issues correctly. Please correct me if there is anything I misunderstood or missed. I refer only to iOS 7 and above, and focus on detection and not connection (Can you connect to a CLBeacon using the iBeacon Monitoring & Ranging API?).
The options for the beacons are clear - Use a general purpose BLE peripheral or use a BLE peripheral that advertises in the iBeacon format (Also, a non-standard peripheral can advertise in the iBeacon format in the adv-packet and a different format in the scan-response packet).
General Restrictions
didRangeBeacons will be called every second with an array of CLBeacon objects that were found recently. The distance from the beacon and its accuracy are calculated by the iOS using some confidential algorithm that only Apple's developers really know (The algorithm is based on the rssi values and the rssi-at-1-meter calibration byte that the beacon advertises). You can also use iBeacon Monitoring to call a delegate every time you enter or exit a region - again you must specify the ProximityUUID that you are looking for (you can also specify a major & minor). "Exiting a region" is defined by some time of not receiving any advertisement, and therefore cannot be immediate. The number of regions that can be ranged\monitored simultaneously per device is limited to 20 - This means that if other apps do monitoring\ranging at the same time, your app may not be able to monitor\range (right?).Running in the Foreground - The less restricted use-case:
nil in the serviceUUIDs of scanForPeripheralsWithServices will scan for all peripherals. Passing CBCentralManagerScanOptionAllowDuplicatesKey as YES in the options will make the didDiscoverPeripheral to be called multiple times for the same peripheral\beacon (I assume that using a timer you detect the advertisement was not received for some time and assume that the user exited the "region"). Running in the Background - The more restricted use-case:
didEnterRegion and give the app runtime of 6 seconds - in which you can start Ranging (for example, to detect major & minor). The detection may not be immediate since iOS turns scanning on and off to preserve the battery power. If you enter a region of multiple beacons with the same ProximityUUID, and you monitor this UUID without a specific major and\or minor, didEnterRegion will be called when you start receiving the signal from the first beacon - however, if you did not exit the region of the first beacon and you also entered the region of a second beacon the app will not be woken up again (didEnterRegion will not be called again) so you cannot start ranging to detect the second beacon's major & minor. The app cannot simply pop up to the foreground, but can create local notifications and other background operations.scanForPeripheralsWithServices can run in the background using, but you must specify at least one serviceUUID. didDiscoverPeripheral will be given a runtime of 10 seconds. Using CBCentralManagerScanOptionAllowDuplicatesKey will not work - didDiscoverPeripheral will be called once for every peripheral. Therefore, you cannot detect "exit" from the region and "re-entry". I suppose you can use a non-standard BLE peripheral that changes its MAC address to overcome this issue. The app cannot simply pop up to the foreground, but can create local notifications and other background operations. The detection may not be immediate since iOS turns scanning on and off to preserve the battery power. Running after the app is killed
Does anyone have more experience with these restrictions? Can scanForPeripheralsWithServices be used as a better alternative to iBeacon Monitoring in some use-cases?
Thanks!
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An iBeacon is a device that emits a Bluetooth signal that can be detected by your devices. Companies can deploy iBeacon devices in environments where proximity detection is a benefit to users, and apps can use the proximity of beacons to determine an appropriate course of action.
Monitoring Beacon Regions. Beacon region monitoring uses an iOS device's onboard radio to detect when the user is in the vicinity of Bluetooth low-energy devices that are advertising iBeacon information.
iBeacon is the name for Apple's technology standard, which allows Mobile Apps (running on both iOS and Android devices) to listen for signals from beacons in the physical world and react accordingly.
The positioning accuracy of the iBeacon-based method is RMSE 2.75 m. When the smartphone is held steadily, the fusion positioning tests result in RMSE of 2.39 and 2.22 m for the two routes. In addition, the other tests with orientation noises can still result in RMSE of 3.48 and 3.66 m.
You are mostly right with your description. Just two clarifications:
The 20 region limit is not per device, it is app-specific. No matter what other apps are doing on the mobile device, your app is still allowed to monitor up to 20 regions by iOS. That said, there are likely hardware limits that are device-specific on how many regions can be monitored in the background with hardware assistance. These limits are undocumented. If you surpass these undocumented limits, it will probably take a lot longer to detected beacons in the background. (Although that said, there is no OS guarantee of when the detections come, anyway.)
You cannot connect to a CLBeacon using Monitoring and Ranging APIs. These APIs only work with BLE advertising packets, which are connectionless.
Yes, it is possible to use scanForPeripheralsWithServices as an alternative. This is what Gimbal beacons do in order to implement a proprietary system. There are real disadvantages, however, in terms of background detection time and reliability.
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