A power tool comprising: an implement located in a predetermined location in the power tool; an actuator configured to move the implement in a predetermined motion during operation of the power tool; an implement arrest mechanism operatively connected to the implement; an ultrasonic emitter and an ultrasonic receiver, the ultrasonic emitter being configured to emit an ultrasonic signal and the ultrasonic receiver being configured to receive an echo return signal from an object that reflects the ultrasonic signal; and a controller operatively connected to the actuator, the ultrasonic emitter, the ultrasonic receiver, and the implement arrest mechanism, the controller being configured to: operate the actuator to move the implement; identify a distance between the implement and an object that is proximate to the implement with reference to data corresponding to an ultrasonic signal emitted from the ultrasonic emitter and an echo return signal received by the ultrasonic receiver; identify a type of the object with reference to an amplitude of the echo return signal; and activate the implement arrest mechanism to stop movement of the implement or move the implement from the predetermined location to prevent contact between the object and the implement while the implement is in motion in response to the identified distance being less than a predetermined threshold and the identified type of the object corresponding to a portion of a human body. an implement located in a predetermined location in the power tool; an actuator configured to move the implement in a predetermined motion during operation of the power tool; an implement arrest mechanism operatively connected to the implement; an ultrasonic emitter and an ultrasonic receiver, the ultrasonic emitter being configured to emit an ultrasonic signal and the ultrasonic receiver being configured to receive an echo return signal from an object that reflects the ultrasonic signal; and a controller operatively connected to the actuator, the ultrasonic emitter, the ultrasonic receiver, and the implement arrest mechanism, the controller being configured to: operate the actuator to move the implement; identify a distance between the implement and an object that is proximate to the implement with reference to data corresponding to an ultrasonic signal emitted from the ultrasonic emitter and an echo return signal received by the ultrasonic receiver; identify a type of the object with reference to an amplitude of the echo return signal; and activate the implement arrest mechanism to stop movement of the implement or move the implement from the predetermined location to prevent contact between the object and the implement while the implement is in motion in response to the identified distance being less than a predetermined threshold and the identified type of the object corresponding to a portion of a human body. operate the actuator to move the implement; identify a distance between the implement and an object that is proximate to the implement with reference to data corresponding to an ultrasonic signal emitted from the ultrasonic emitter and an echo return signal received by the ultrasonic receiver; identify a type of the object with reference to an amplitude of the echo return signal; and activate the implement arrest mechanism to stop movement of the implement or move the implement from the predetermined location to prevent contact between the object and the implement while the implement is in motion in response to the identified distance being less than a predetermined threshold and the identified type of the object corresponding to a portion of a human body.