posture biofeedback

The Perseus PostureTek seems to be a special shirt that detects and alerts you when you slump. Presumably it senses the tension in the "filaments" (an X-shaped string across the chest and back). The "mechanism" is a knob that screws into the side of the shirt, which determines how sensitive the device will be, and which vibrates when you slump.

Their website is remarkably opaque: all the relevant info is in the second half of their video.

The shirts sell for around US$130. I'm very tempted to buy one, but I want to learn more first.

I'm concerned that the device's sensitivity depends on the filament being uncomfortably snug.