The Garmin nav units are able to pair with either BC30 or BC40 or both - I don't know if that's universal across all Garmin dash nav units but I'm pretty sure it's almost all of them. Older Garmins that don't have built in wifi can't pair with the BC40.
BC30
Some Garmin nav units require the use of a receiver built into the power cable, which is included in the
BC30 kit but once you have that cable it also can pair with multiple BC30 cameras so you could select whichever one you want onscreen. If you have a newer Garmin nav unit you may not need the cable and can just pair the unit straight with the
add-on camera . The BC30 camera is small but connects to a transmitter that can be mounted anywhere, powered by +12v and begins transmitting whenever it is supplied with power. You can wire it to your reverse lights so when you shift into reverse, the camera gets power and turns on and the nav unit begins displaying the video. In other words, works like a factory reversing camera. This is how I have it set up in my Ram, with the camera itself installed hidden in the location where a factory reversing cam would be. If you wanted a front bumper cam for parking, or rock cameras or a load camera for your trailer, etc just set them up with switched power and that's it. I don't remember the limit for how many you can pair but I'm pretty sure it's at least 4 cameras.
Incidentally, if your Garmin unit supports traffic/weather but didn't come with the traffic receiver cable, the camera receiver cable also will enable HD traffic and limited weather/alert functionality in your nav unit.
BC40
This camera is battery operated and requires no wiring to install. It is compatible only with newer Garmin nav units that have wifi built in. (Newer Garmin units also use wifi to update themselves so you don't have to bring them in the house and plug them into a USB port to update them periodically if your wifi extends to the garage..) . The BC40 doesn't automagically activate when you shift into reverse but can be selected from the on screen menu or activated by voice command. I believe the
BC40 also has higher resolution than the BC30, but this is also dependent on the nav unit you use because for example the
drivesmart 51 has pretty low resolution while the almost identical
driveluxe 51 has a much sharper LCD .
For what it's worth, I have a NuviCAM (older, non wifi, with constant recording forward dashcam) in my Ram using a BC30 as a reversing camera. I have the camera hooked up to the reverse light circuit in my 7 pin trailer wiring harness. Connection is wireless between the camera and the nav unit so no new wires run into the cab, etc. It's been flawless going on 5.5 years. I also have a Drivesmart 51 in my other car(s) ... it's been doing its thing across several vehicles and works awesome with the BC40. I have not attempted to use both a BC40 and a BC30 on the same vehicle but I believe on modern, BC40 compatible nav units you can use both. So, for example you could have a BC30 on the rear of the vehicle as an automatic reversing camera and also have a BC40 in the front as a parking/rock crawling camera activated by voice command or onscreen menu selection. If you get one of the newer dashcam units like a
DriveAssist for example you could have the always recording forward dashcam plus any combination of BC30 and BC40's wherever they're useful.
I hope that helps.
(There is also a BC35 camera, it appears to be almost identical to the BC30 but has a different field of view - however it is only officially compatible with a small group of commercial trucking focused nav units. I don't think it can be used with the non-trucking-focused nav units)