I will be participating in Lagoon Physics Day and I will be testing a homemade accelerometer. I don't know how to make one to fit Physics Day expectations. Can anyone help? Requirements:

Width: 8 cm Length: 20 cm Height: 10 cm Weight: less than .5 kg

Must be securely attached to operator (like a wrist watch) and be hands free.

No Glass, separating parts, or harmful chemicals

Thanks