Vibration Sensor Double Ball Rolling Electronic Shaking Switch
10 pcs for ~80 cents US. I tested some, very
sensitive to tilt. Works just like a mercury switch with much less hysteresis (stiction), not to mention more environmentally friendly. I measured ~0.5 ohms at a very slight tilt. I'll hoard more of these "poor man's accelerometers". When shaken (not stirred) you can hear the balls inside a bit. ~0.500" long x 0.150" dia.
Related: just saw these and ordered. Sounds like it has a vibration contact spring inside instead of balls. 20 for a buck is worth checking out IMO: http://www.ebay.com/itm/201070228446