In an example, a mobile device is configured to automatically lock when a detector, such as a GPS receiver, determines that the device is in motion above a certain speed threshold, such as 10 mph. Additional detectors may be used to determine whether the device is operated by the user or by a passenger, so that intelligent decisions can be made about whether to lock the device. During the lock, certain selected apps such as a GPS navigation system or music player may be enabled, with limited controls as appropriate. In some cases, hands-free operations may be available. The mobile device may also be configured to provide an automated response to incoming calls and messages.