The actual implementation to have a enduring connection (over serial port I guess) powers the battery of the phone down very quick.
Is it possible to only query for the existence of the phone instead of creating a direct connection?
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actually it *should* not really drown the battery since the channel is only created but no actual transmission is made at any time. Querying the existence of the phone gives poor performance since it is not possible to check for the distance. That is bluetooth 1.1, 2.0 wants to deliver the rssi value while doing a scan but I wanted to create a tool compatible to every device around there and I also have no experience with that feature. Also having the notebook detect only the presence of a certain mac address there would be serious security issues arising. To do "an attack" one would only need to clone the mac address of the detected device. While the original device is away your fake device approaches and bang - your computer is open to anybody. Using a connection requires a pairing and that should require some interaction on the desktop. Once paired both sides have created a secret pairing key sorely for that paired device. That way cloning the mac is not useful for the attacker.
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I see you're right with that security issue. I agree with you.
Just to comment your not about the "unpowering" of my phone. I have a SE K750i which, with bluetooth enabled (not visible) and not connected to something, I can use for about one week, but connected to my laptop (with BlueProximity) it only lasts 2, max 3 days.
Therefore I found the other solution "better", but the security issue is much to important.
Hm, that still is a big power drain. Maybe we can try to find out whether it would be an "energy saving mode" if I would disconnect immediately after checking the rssi value. Connecting takes about 2 seconds so if checks are only done every 5 secs it would give 3 secs without a connection. I would think that the connecting process takes more power than keeping up the connection but that would be a point worth testing. Of course only checking every 5 secs is much less accurate since leveling over a period of time does not really work since you may only take the last 2 or 3 values into account. (Or else you increase the time to the first detection of the "away" signal) There might be another point against this. I have noticed (with my nokia) that directly after connecting, even if the phone is far away, the rssi value is 0 and afterwards moves back to a greater value. I think that the bluetooth rssi algorithm is responsible for that but once again that might be worth testing...
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