Trying to use Bluetooth to pair a device like a headset or keyboard, but keep being asked for an unknown four-digit passcode? Long experience suggests that it's very likely to be 0000, 1234 or (a tad more rarely) 9999.
Picture by Neil T
Having such obvious passwords is, of course, a major security no-no in general terms. But for Bluetooth devices such as headsets, security often takes second place to convenience, and on cheaper devices, you may not have the option of changing the code anyway. If you're a Bluetooth veteran, this is rather obvious advice, but it's worth noting for newbies.