I have to dash away from the computer frequently, and I want to trigger some commands to run when my iPhone is close enough/far enough from my iMac (next to it vs. 2-3 metres away/other side of a wall). A couple of minutes latency is fine.
I've downloaded reduxcomputing-proximity and it works, but this only triggers when the device goes in to/out of range of bluetooth, but my desired range is much smaller.
(Proximity polls [IOBluetoothDevice -remoteNameRequest] to see if the device is in bluetooth range or not.)
I've used [IOBluetoothDevice -rawRSSI] to get the RSSI when I am connected to the iPhone (when disconnected this just returns +127), but in order to save the battery life of my iPhone I'd rather avoid establishing a full bluetooth connection.
Am I correct in thinking that maintaining a connection will consume more battery life than just polling every couple of minutes?
I've overridden the isInRange method of proximity here to give me a working solution that's probably relatively battery intensive compared to the previous remoteNameRequest: method:
- (BOOL)isInRange {
BluetoothHCIRSSIValue RSSI = 127; /* Valid Range: -127 to +20 */
if (device) {
if (![device isConnected]) {
[device openConnection];
}
if ([device isConnected]) {
RSSI = [device rawRSSI];
[device closeConnection];
}
}
return (RSSI >= -60 && RSSI <= 20);
}
(Proximity uses synchronous calls - if and when I fit it to my needs I will edit it to be asynchronous but for now that's not important.)
This SO post references getting an RSSI during an 'inquiry scan' which sounds like what I want, but it talks about using the Linux Bluez library, whilst I am on a Mac - I'd rather do it without having to stray too far if possible! (I have considered using a VM with USB pass-thru to hook up a second bluetooth device... But a simpler solution would be preferable!)
I see there is a IOBluetoothDeviceInquiry class, but I am not sure if this is useful to me. I don't intend to learn bluetooth protocol just for this simple problem!
For interest, and not particularly relevant to the solution, here are the Apple Scripts I currently trigger when
in range:
tell application "Skype"
send command "SET USERSTATUS ONLINE" script name "X"
do shell script "afplay '/System/Library/Sounds/Blow.aiff'"
end tell
out of range:
tell application "Skype"
send command "SET USERSTATUS AWAY" script name "X"
do shell script "afplay '/System/Library/Sounds/Basso.aiff'"
end tell
Though these are likely to get longer!
In terms of tradeoffs for your use case doing a continuous or periodic inquiry will consume same or even a bit more energy as doing a periodic connect / read RSSI and disconnect. Depending on the use case it sometimes may be more efficient to maintain the connection in a low power mode (sniff with 2.56 sec interval) and remain connected if the device is in range. And use RSSI to monitor proximity (although it is not accurate as interference due to objects change rssi drastically even though the device might be in proximity)