I'd like to develop a battery powered Arduino (ATMEGA328) for sensing orientation and movement, and wirelessly transmit the fact that movement has been detected. Does anyone know of a good mechanical sensor for sensing orientation? Since this is battery powered, I can't use one of those 3-axis magnetometer or accelerometer because the ATMEGA328 will be sleeping most of the time. I need something that can generate a interrupt, like those shake sensors.
What do you actually want to do? If the object is shaken to generate a wakeup, it may be very difficult to define an orientation.
Some accelerometers are quite low power, and can be programmed to signal an interrupt (a wakeup) if the acceleration exceeds a specific value, or is close to zero (as in free fall). Here is an overview http://www.planetanalog.com/document.asp?doc_id=528265
You haven't given any indication of any size limitations (does the device have to be very small?) or the amount of movement you want to detect. Another potentially important issue with mechanical sensors is whether the device is carefully placed (straight and level and upright) in its normal position.
I'm wondering is some form of pendulum would work?
As a followup to what Robin wrote.
There are devices like Mercury Tilt switches (https://en.wikipedia.org/wiki/Mercury_switch) , that can detect tilt and other movements, but the object has to be placed on a level surface, otherwise the Murcury could be in contact with internal connections all the time.
There are also sensors like this http://www.alibaba.com/product-detail/Micro-waterproof-Omnidirectional-Motion-sensor-mechanical_1799125394.html
But the movement required to trigger them may be too high for you