I’ve been using Target Display Mode often over the past couple of months, using my iMac screen as a display for my MacBook. This solved the problem of shuttling video and other files between the two devices – now I do almost everything on my MacBook, while I still have the iMac there when I need it. Since Target Display Mode doesn’t let you share a keyboard and mouse/trackpad, and since you can’t control your iMac to turn off Blutooth once you initiate Target Display Mode, I went off in a search of a solution.
My initial plan was to get a Logitech Bluetooth Easy-Switch K811 Keyboard. Amazon reviews suggest, however, that this keyboard can’t initiate Target Display Mode. That made it unusable for my purposes, so it was back to the drawing board.
I then found a workable solution. James Holland has a write up on his blog for how to use a PowerMate to toggle Bluetooth off on your iMac (when you want to use Target Display Mode) and on (when you want to use your iMac on its own).
This works for me, but it isn’t bulletproof. I’ve found that the long press on the PowerMate to deactivate Bluetooth isn’t reliable. Sometimes it just doesn’t register. I have to keep a spare keyboard and mouse nearby as a backup, which defeats the purpose for having the PowerMate.
Over in the comments to the post at JamesHolland.com, you’ll see that I asked how he gets his MacBook to release the Bluetooth devices when he’s ready to turn control back over to his iMac. I don’t know how he does it, but now when I’m ready to deactivate Target Display Mode, I unplug the Thunderbolt cable and then disable Bluetooth on the MacBook. That frees up the keyboard and trackpad, so that the iMac can grab them after I do a long press on the PowerMate.
if you decide to try this, make sure you get the USB version of the Powerate, and then head off to the post by James Holland for all the details.
∞ Hacking Mac OS X to toggle Bluetooth for better Target Display Mode | JamesHolland.com