Aniomagic built this weight-sensitive backpack and writes:

I’ve been traveling a lot with my backpack, sometimes putting too much in it, which is bad for my back. Taking a cue from this weight-sensing tote on Instructables , I decided to build one using schemer.

Schemer is a tiny programmable button that helps you easily make interactive art and craft. Instead of using wires or bluetooth, you program it by holding it in front of a computer screen. You only need your web browser. No wires, and no extra hardware or software to install.

With the schemer web interface on my iPhone, I can quickly calibrate it for my needs, or make it do random flashing patterns anytime I want, without breaking out a USB cable or anything. The 3 volt felt battery holder is eye-catching too, no?