Small, mobile devices without user interfaces, such as Bluetooth headsets,often need to communicate securely over wireless networks. Activeattacks can only be prevented by authenticating wireless communication,which is problematic when devices do not have any a priori informationabout each other. We introduce a new method for device-to-deviceauthentication by shaking devices together. This paper describestwo protocols for combining cryptographic authentication techniqueswith known methods of accelerometer data analysis to the effect ofgenerating authenticated, secret keys. The protocols differ in theirdesign, one being more conservative from a security point of view,while the other allows more dynamic interactions. Three experimentsare used to optimize and validate our proposed authentication method.