A cheap non-contact voltage detector

I impulse bought this non-contact voltage detector from Aliexpress because it was 70p, including postage. I thought I might even just use the case to make some other type of probe, like a static field probe.

As it arrived, it worked, but the battery cover did not stay on securely. This would be a bit concerning for using it near live parts. Cutting down a wire and bending the securing tab improved the situation.

The button is not an on/off switch, as it is on the Fluke whose appearance was copied. The device is always on, and the switch lights an LED. Current draw measured at 3.5uA quiescent with multimeter, but it would not operate with uAmmeter in circuit. Uses nearly 3mA when beeping quietly (with 470R in buzzer circuit).

There are very few components. The probe goes straight into the unmarked IC. I guess it may be an ASIC. Maybe it is possible with a microcontroller with high enough input impedance? There is a transistor marked J3Y. There are no capacitors at all, not even a bypass cap.

The beeper is very loud and upset several people in the room when I was testing it. I turned down the volume by adding a resistor in the line to the buzzer. With 470 ohms, it is probably a bit quiet. Maybe 330 or even 220 would be better.

Advertised as: “Electric indicator 90-1000V Non-Contact Socket Wall AC Power Outlet Voltage Detector Sensor Tester Pen LED light AC 110V-220V” (https://www.aliexpress.com/item/1005009692871069.html)