Various systems and methods for selectively controlling the activation of an ultrasonic surgical instrument according to the presence of tissue within an end effector are disclosed. A control circuit can be configured to determine whether tissue is present within the end effector and permit activation of the ultrasonic transducer at a power level according to whether tissue is present within the end effector. In some aspects, the control circuit can be configured to automatically activate the ultrasonic transducer in response to tissue being detected within the end effector.