Wondering if anyone has been keeping an eye on the new emergency of lower-power, Bluetooth 4.0 devices that are aimed at connected devices and feature quick negotiation and connection. For about $30 the Tod device on Kickstarter (now funded) looks interesting. It would seem idea to leave a few of such devices around the home, in the garage, etc. and then trigger Indigo actions or set variables based on a proximity reading with an iPhone or other device.
Adam