Embodiments of the invention may use a first accelerometer to measure first acceleration data of a first device. Other interaction data, including time data and geographic location data, generated by the first device may also be recorded. First acceleration data is compared by a remote server computer to second acceleration data generated by a second accelerometer in a second device. If the first and second accelerometer data are substantially equal, it can be determined that the devices have interacted and communications can be initiated. After communications are initiated, a financial transaction is conducted. Accelerometer data may be stored and / or used as part of the authentication process in a payment processing network. Other embodiments of the invention use the accelerometer to generate movement security data to make financial transaction more secure. Accelerometer data is used for authentication, security, encryption, session keys, non-repudiation, or fraud protection.