i failed to mention the most important aspect of the project: (near) zero power consumption when idle.
it is a vacuum (that kinda looks like r2d2) that i want to play some r2d2 noises when used.
it is hauled around on a construction site on the scaffolding and wont be in an upright position while idle or in usage, so tilt switches didnt make sense to me.
i plan to run it from a coincell or maybe 2 aa, but it should only draw power when the sensor is triggered so the power should last years if i understood the 555 timer correctly. that means accelerometers and linear hall effect sensors are out too due to microcontrollers and thus power draw.
somebody else mentioned vibration sensors (SW-18010) that look promising.