I need to build a simple accelerometer wrist watch to record hand or leg movements during sleep and get ( X,Y Z) data. How can I start with this ?
Buy an accelerometer and a microcontroller, and learn how to use them.
how can I interface them ?
With wires, preferably short.
There are many, many articles on the internet that you can find to satisfy the “… and learn how to use them” suggestion.
Use that thing called ‘Google’ and type in the search area "interface accelerometer with " and you will have may different things to choose from.
Also, you may want to read the article on "How to ask questions the smart way::