Abstract: Techniques are disclosed for validating input on a handheld device. In response to receiving an input and a request to access a computing resource, an application running on the handheld device may collect data from one or more sensors of the handheld device. The application may then determine, based on the collected sensor data, if an individual is interacting with the device and recognize the input as valid if such is the case. In one embodiment, the application may present a challenge to a user which is difficult for computer programs to perform, and determine whether an individual is interacting with the device based on successful completion of the challenge. In an alternative embodiment, the application may collect data and determine whether an individual is interacting with the device without presenting an explicit challenge to the user.