How do we know when to turn systems back on?

One very important affordance that I want Mezzo to offer is the ability to determine when a guest's stay is over.

If Mezzo simply allows visitors to disable the homeowner's listening devices, it's not nearly as desirable: this means that there owner has to remember to "clean up" after their guests and re-activate each device, and that's a lot of extra work.

I worked for quite some time on the idea that I could keep a running list of observed electronic devices by observing wireless probe requests. Put simply, this means I would have a little observer-script always running on my router, and it would look at the regularity of probe requests from unique devices. When a device had not been heard from in some amount of time, we would strike it from our running list of "present" devices and assume whoever was carrying that cellphone/iPad/etc had left.

Knowing this, I contrived a heuristic that would roughly associate "new" and "just-arrived" MAC addresses with incoming interactions to the Mezzo UI interface. Thus, when Mezzo got a "please disable system FOO" request, we could look at the list of recently-arrived guests and make a note to restore system FOO when those guests had left.

But!

Do you see the silly, basic problem that makes this an insufficient solution?

Dear reader, you should not have to own or use an electronic device in order to be "counted" by my system!

Embarrassingly, I went quite a ways down this path (some sketching that may be interesting to you is here) before I realized I needed a more inclusive solution. It's early days, so this may change, but my options seem to be:

• Allow guests to specify the time that systems will be disabled, with a generous default like 2 hours (or a default settable by the homeowner)
• Use an identification technology to actively view incoming and departing guests (the ironies here of using something like facial recognition to track users of a privacy device are multifoliate, so I will probably not pursue this (although a counterpoint is, if this system runs entirely on a local subnet and is put to good use, that's precisely where the "good" parts of those technologies have the most impact))
• Use simple motion-detection technology to identify warm bodies moving into or out of the space

...for now, I think the simple motion-detection is the way to go (my studio is brimming with different kinds of motion sensors, including some neat thermal cameras), but there are some complexities that I'll go into in future posts.

One affordance I think is certainly necessary for all implementations is an unambiguous audible chime indicating that listening systems are being turned back on; this way if there is a false positive (we think the guest has gone, but he/she is still present), the participants will know immediately and be able to act on this.