On my mac I have to wake up the Bluetooth keyboard first while the screen is still gray. Once it's awake then I can use all of the normal commands.

I use this mostly to get into bootcamp. I reboot the mac, when the screen is gray but before the apple logo appears I tap the power button on the bluetooth keyboard to wake it up. Then I hold down option to select my bootcamp partition.

But the same pattern works when using the other boot time keys such as getting into single user mode, booting from DVD, etc.

Thank you, thank you, thank you!!!!

I have a new 27" iMac with a Bluetooth keyboard and the stupid Apple tech support could not give me the advice you just did!

For months whenever I needed to startup in SUM or use Target Disk Mode I had to use my cabled Apple keyboard.

Again... thanks!

Hitting the side power button on the iMac keyboard at just the right time allows the keys to be used at startup.

I had done extensive searches on this subject and could not find the answer anywhere until just now.