An ultrasonic surgical instrument (12) having a deflection detection circuit (200) is disclosed. The instrument includes an ultrasonic probe (21) configured to conduct electricity and positioned a predetermined distance from one or more tubes (46). The ultrasonic probe is adapted to be operatively connected to an ultrasonic generator (14) for vibration. The instrument also includes a deflection detection circuit having a secondary power source (202) and an indicator (204), the power source is configured to supply electrical current to the tube, the probe, and the indicator, wherein the circuit is configured to close in response to the probe contacting the tube when the probe is deflected toward the tube thereby activating the indicator.
