I guess you could do the same, but shut down the computer instead.
I had a program like this back in PowerBook days. It automatically unlocked the computer if a specified Bluetooth signal reached a particular strength, and locked the computer again if the signal strength fell below another threshold.
It worked great, when it worked. It had maybe a 70% success rate, but that was good enough.
unless they hit you with the cryo, too.
A more sophisticated implementation could be done if you can write software on the device. A PineTime would be perfect for this.
I am not sure why mention iOS specifically, a phone is easily forgettable. Moreover, you don't really need to rely on any location API provided by the system, even if UWB or Bluetooth Location Services would do wonders for this, a simple RTT latency measurement or RSSI value should be enough.
I also got multiple LG watch R, I'm probably going to fiddle a bit with them when I have time, hopefully mainlining them and porting postmarketos over. I'm open to trying again with those. In the end, I don't really have sensitive documents on a laptop (besides work-related confidential stuff), so I'm not sure I'd crank paranoia to 11.
As for my phone, I often pull it out of my pocket and leave it on my desk, or abandon it somewhere, charging or powered off -- I should probably be more careful with that, but people know to expect some latency when contacting me.
Both the dongle and the computer have accelerometer-bump-tilt-oh-fuck-support.
A OTP has to be entered every 5 minutes, or a secure screen/dead sequence starts.
Sudden accelerated movements or a lack of presence-detection would also start the sequence.