Non-contact voltage detectors make it easy to find broken parts in series circuits. (ex. Christmas tree string light)
In this video, twenty of 12V car bulbs connected in series and powered by AC 220V main voltage.
Quickly find a failed bulb using a non-contact detector.
Non-contact voltage detector is only working AC voltage. So, can not detect DC Voltage. Do not judge the risk with a non-contact detector alone.