Not sure what your issue is. I have a pretty low-end Zircon that has been
used faithfully for years. Unlike the current crop with lots of different
LED's for the differing densities, mine has TWO. Still works 99% of the
time.

Studfinders are, by the way, pretty useless on plaster walls. On sheetrock,
you have to make sure you start where there isn't a stud (trial and error)
for it to work, as it will "calibrate" on the non-stud when you push the
button.

-Tim