There are a lot of ways to communicate wirelessly, from your mobile phone's connection with cell towers to your computer's Wi-Fi internet connection. Bluetooth works much the same way as these technologies, except over shorter distances and with much lower power consumption. Some Bluetooth devices connect without you knowing or caring how, just like your cellphone. Others require a password, like your Wi-Fi.
What Happens When You're Pairing
Bluetooth devices connect to each other through a process called pairing. You start by putting your accessory in "discoverable" mode, which is the electronic equivalent of waving and trying to catch someone's eye from across the room. Then you'll tell your main device – a phone, a computer, or whatever – to search for it and pair up. When they locate each other and exchange their identifying information, they form an encrypted connection and trust each other to communicate in the future without needing to pair again. With newer devices, pairing usually happens automatically without any input from you. Older or lower-end devices may prompt you to enter a PIN as part of the pairing process. That's where things get interesting.
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Use the Default Bluetooth PIN
Before you get too caught up in trying to find the Bluetooth passkey for your specific device, it's a good idea to start with one of the small handful of generic PINs. A lot of devices, especially small "dumb" gadgets with only one or two functions, use these. The most common PIN is four zeroes in a row, 0000. Two others you may encounter on some devices are 1111 and 1234. Try entering those when you're prompted for a PIN, starting with 0000, and most of the time, the pairing finishes successfully. If it doesn't, that's the time to start digging a bit deeper.
The Usual Suspects
Start by giving the device itself a close look. If it requires a Bluetooth pairing code, there's a chance it is imprinted on the device somewhere, perhaps on a decal on the underside or in the battery compartment. If you're the kind of person who keeps manuals, start burrowing into your files to see if you can find the instructions that came with your device. They almost invariably include your Bluetooth PIN. If you don't find one there, search your device's manufacturer online. You might be able to find that information on the website, or at least find a tech support line you can call. If all else fails, searching the internet for your device's model number along with phrases like "Bluetooth passkey," "Bluetooth password" or "Bluetooth PIN" often does the trick.
Programmable Bluetooth PIN
Where things get interesting is with devices that have a Bluetooth PIN that's programmable so you can choose your own as an added security feature. If you forget the passcode you've chosen or if you buy a used device with someone else's PIN on it, you can't rely on finding a default passcode to use. Instead, you need to look up the reset procedure for your particular device. You may be given the option of clearing the personalized PIN and returning to the default or of overwriting the previous PIN with one of your own.