Here is a quick 'teardown' of the "Marksman Multi-Function Electronic Tester" available on eBay for a few quid. It promises to do pretty much everything! I bought it as a cheapo NC voltage detector - I don't really know why, it wasn't going to be an improvement on my Fluke. I did like the idea of its continuity testing feature though.
As you can see, there is nothing at all variable, both of the switch positions for Non-contact mode connect the exact same pins!
For the rest of it, there's a darlington pair and a couple of resistors with the red LED, and a 4069 CMOS hex inverter for the Green. Two gates to detect, two as an oscillator to make the speaker go BEEEEEEEEEEP (a little under 4KHz with those component values if you were wondering)
Maybe I got a fake one or something, maybe it is just typical Chinese crappy electronics that shouldn't be allowed to be sold.