Bluetooth has many different pairing modes. The one most commonly used by pin-less devices like headphones and speakers is called Secure Simple Pairing. It pret

Bluetooth has many different pairing modes. The one most commonly used by pin-less devices like headphones and speakers is called Secure Simple Pairing. It pretty much just accepts any connection. There are other modes depending on hardware availability. If the device only has a screen there's a mode where it displays a pin for you to enter on the host. If it only has input but no screen, the host can give you a pin to enter on the device. The pin can be hardcoded (as with '0000') or generated on the fly. You can also have a pin-less device respond to pairing requests with a hardcoded pin, or obtain the pin through some side channel like a separate radio or a wired connection. In all cases, the devices typically use diffe-hillman to negotiate a secure link after pairing. You do have the option to disable encryption. Additionally, "pairable" and "visible" are totally independent concepts. A device can be "invisible" but still accept pairing from a device that knows its address. You can also be visible without accepting pair requests. This part of the BT spec was actually thought out quite extensively. There seems to be a provision for every corner case I've been able to imagine. No matter your situation, there's always a mode you can use to get your connection up.