Smartphone sensor - accelerometer

I came across a good discussion of this in the "Quantum Progress" blog - a blog which seems to be really useful for Physics teachers in general. The accelerometer is not what one might initially expect...

"The first thing students noticed that was strange is that even when the phone was sitting completely still, which should be an acceleration of zero, the phone would read an acceleration in the vicinity of 10 m/s2. " 

See the article for the explanation.