Abstract: In various embodiments, a method for determining a match between two devices includes receiving sensor data from a first device and a second device, determining whether the sensor data indicates a match between the first and second devices. If there is a match between the first and second devices, the match is confirmed. The match is confirmed based on at least one of: at least one knock, analysis of missing information and a characteristic of a user of the first device or a user of the second device. In various embodiments, a method of activating a function includes receiving sensor reading(s), analyzing the sensor reading(s) including determining whether at least one knock has occurred based on the sensor reading(s), determining whether to activate the function based on the analysis. If the function should be activated, the function is activated.