Well, I know that, most of the time,
electronic devices can handle over-voltages
of several volts and not burn-out, but what
X-10 motion sensor uses 6 volts? I might see
if I could find a 3, or 4.5 volt adapter.
Six volts probably wouldn't hurt anything,
though. Anyway, it should work just fine,
making sure you've got the polarity correct.