Core Bluetooth - constant RSSI updates of in-range devices

Have you tried changing the scan option to YES?

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber  numberWithBool:YES], CBCentralManagerScanOptionAllowDuplicatesKey, nil];
[manager scanForPeripheralsWithServices:nil options:options];

If you do this you will get your "didDiscoverPeripheral" callback with every ad packet that is seen by your iPhone, which would normally be about every 100ms (although I see this callback timing varying a lot for the same device). This includes the RSSI of each device it sees.

This should be a lot faster than your ~1 minute update rate.

Swift Implementation of @Anders solution:

manager.scanForPeripheralsWithServices(nil, options: [CBCentralManagerScanOptionAllowDuplicatesKey : NSNumber(value: true)])

Is far as I can see, this should do what you want.

When you started scanning for peripherals with the original call, your delegate should begin to get calls whenever a BLE device is discovered. This will continue until you stop the scan with a call to

[manager stopScan];

I don't think you actually need the second call to scanForPeripheralsWithServices in your centralManager:didRetrievePeripherals method, since, as far as I know, the scanning doesn't stop until you tell it to. I'm still getting started on this, too, though, and there may be a timeout I have not found, yet.

I'm pretty sure the reason you get a call about once a minute is because the BLE device is only advertising that often. If it advertises more often, like a device in discovery mode, I think you will get the calls more often. I would be interesting if you could confirm that. If the device has a discovery mode, you might try triggering it to see if the notices speed up.

You shouldn't do continous scanning as it is very costly for power. Once you discovered devices you have an array of CBPeripheral objects returned to you. On CBPeripheral you can read RSSI and get a callback when RSSI changes. See the following documentation: http://developer.apple.com/library/mac/#documentation/CoreBluetooth/Reference/CBPeripheralDelegate_Protocol/translated_content/CBPeripheralDelegate.html