An ultrasonic surgical instrument includes a first modular assembly including at least one operator input feature an ultrasonic transducer supported by the first modular assembly, and a second modular assembly configured to be removably coupled with the first modular assembly. The second modular assembly includes at least a portion of an end effector extending distally from a distal end portion of the second modular assembly. The instrument includes a mechanical lockout assembly configured to switch between at least an unlocked configuration and a locked configuration. In the locked configuration, the first modular assembly and the second modular assembly are partially coupled together such that the operator is physically prevented from activating the instrument using the operator input feature. In the unlocked configuration, the first modular assembly and the second modular assembly are completely coupled together and the operator is able to activate the instrument using the operator input feature.
