Bluetooth is a short-range, low-power, wireless cable-elimination technology. It’s designed to connect gadgets in pairings that make sense, like cellphone+earpiece, Mac+wireless keyboard, phone+portable speaker, or Mac+cellphone. In Sierra, Bluetooth is the key to the Continuity features described in Chapter 9; it’s the wireless link between your Mac and your iPhone.
Now, you wouldn’t want the guy in the next cubicle to be able to operate your Mac using his Bluetooth keyboard. So the first step in any Bluetooth relationship is pairing, or formally introducing the two gadgets that will be communicating. Figure 10-10 shows how that goes.
To do that, open System Preferences→Bluetooth. Make sure that Bluetooth is On. (The only reason to turn it off is to save laptop battery power.)
You don’t have to turn on a Discoverable switch to make the Mac “visible” to other Bluetooth gadgets in range; whenever the Bluetooth pane of System Preferences is open, it’s discoverable.
In fact, you don’t have to click some Add New Device button, either. When the Bluetooth pane is open, the Mac automatically starts searching for nearby Bluetooth gadgets within range (see Figure 10-10, bottom)—nearby headsets, laptops, cellphones, and so on. Usually, it finds the one you’re trying to pair. Just click the one you want, and then click Pair.
When it’s all over, the new gadget is listed in the panel, in the list of Bluetooth stuff that you’ve previously introduced to this Mac. (You can click it and then click 
to get rid of the pairing, when that day comes.)
A few footnotes:
If you’re pairing a mobile phone or something else that has a keypad or a keyboard, the Mac may display a large, multiple-digit passcode. It’s like a password, except that you’ll have to input it only this once, to confirm that you are the true owner of both the Mac and the gadget. (If it weren’t for this passcode business, some guy next to you at the airport could enjoy free laptop Internet access through the cellphone in your pocket.)
At this point, the phone, computer, or palmtop displays a message to the effect that you have 30 seconds to type that passcode. Do it. When the gadget asks if you want to pair with the Mac and connect to it, say yes. (If you’re pairing one Mac with another, just click Continue on both machines; you see the same passcode on both but don’t have to type it.)
If you intend to send a file to another Mac, set up that other machine by visiting System Preferences→Sharing; turn on Bluetooth Sharing.
If you click Advanced, you arrive at a few more tweaky Bluetoothisms:
Open Bluetooth Setup Assistant at startup if no keyboard is detected. Here’s where you can tell the Bluetooth Setup Assistant to open up automatically when the Mac thinks no keyboard is attached (because it assumes that you have a wireless Bluetooth keyboard that has yet to be set up).
Open Bluetooth Setup Assistant at startup if no mouse or trackpad is detected. Same deal, this time suggesting that the assistant will open if the Mac can’t find a trackpad or mouse. Once again, the Mac is assuming that you’ll be wanting to connect a wireless one.
Allow Bluetooth devices to wake this computer. Turn this on if you want to be able to wake a sleeping Mac when you press a key, just like a wired keyboard does.
The Bluetooth menulet (Figure 10-10, top) gives you an easy way to turn Bluetooth on and off, to connect to Bluetooth gadgets, to disconnect from them, and to send files to them (Via Bluetooth). If you don’t see this menulet, then turn on “Show Bluetooth in menu bar” (Figure 10-10, bottom).