iOS: detect app users nearby

Question

I want to build and app which can detect other iPhones with my app within 65 feet range. As I understand I have the following choices:

1. Use Bluetooth to check periodically whether there is device with my app in the range. Send list of found devices to the server. The problem here is battery consumption. Is it true that Bluetooth will be disabled after some period of time automatically?

2. Can I use BLE technology for this purpose? If so, do you know what devices support BLE?

What is the best option on your opinion? Did I miss some other option?

Thanks

UPDATE I plan to run search every 20 seconds or even more often.

Answer 1

One possible solution would to have have every single device send their locations to your server every predetermined time period (more frequent the better but more resource intensive). Then, query the data from the server and get the location of all the devices near you.

Keep in mind, that this probably won't be very useful for real-time data collection. For example, if you want to send data every 30 seconds or so, this isn't a good option.

Use this option if you want to get data every 15-20 minutes or so.

Answer 2

There is no simple answer to this problem.

Bluetooth has 2 flavors: "Regular" bluetooth, used for hands-free devices, headphones, and the like, and BLE (Bluetooth Low Energy)

Regular bluetooth devices must be paired. (I'm less familiar with regular bluetooth than BLE, so take my explanation of this bit with a grain of salt.) In order to be paired they have to be put into "discoverable" mode, which broadcasts their ID. That is a battery-draining and only done briefly. It's not an "always on" solution.

BLE has a range of up to 60 meters, so it should meet your need in that regard.

BLE devices can "advertise" as a "peripheral" for extended periods. Other Bluetooth devices can act as a "central" and ask to be notified when certain peripheral devices are detected. I'm not sure if you can make an iOS device advertise (broadcast) as a BLE peripheral while it's in the background and/or if the device is locked, but it will certainly advertise while it's running. I'm pretty sure you can register to be notified when you detect a certain BLE peripheral from the background, but not positive.

iBeacons are a specific use of BLE with some extra limitations and some extra abilities. An iBeacon is a dirt-simple transmitter that sends a UUID plus a major and minor value and a signal strength calibration value periodically (usually once a second.) You can't add any other data to an iBeacon transmission. iOS can only act as an iBeacon transmitter when the app is in the foreground. If your app moves to the background, it stops transmitting. Period.

However, you can listen for iBeacon signals even from the background. AND, if you've registered as a listener for an iBeacon and the system terminates your app due to low memory, the system still listens for those beacons on your behalf. If iOS detects a beacon you're listening for, you get re-launched if needed, and notified in the background. You can then post a local notification to get the user's attention.

iBeacons are probably your best bet, but you will need your users to be actively running your app in the foreground in order to transmit a signal. That will drain your user's battery fairly quickly.