Is is possible somehow to distinguish between the phone being off or sleeping without turning it on in the process (this happens when pressing the power button)?
I appreciate that I can just use silent or airplane mode rather than turning it off, but was interested to see if there was a way.
This is for the HTC 1. You'll have to see if it works for you. The charge light is red when the phone is off, and orange when it's on. Obviously, that's with the charger connected.
There are a number of "Shake to Wake" apps in the Market. Obviously if you use one of those, shake the phone and it doesn't wake up, then it's fully off.
You can make a call to your own phone number, it is faster than suffering a boot/shutdown cycle.
Also, you can keep some notification just to keep the LED always blinking.
It is a bit of a hassle, huh. There is a slightly unusual solution though: Turn the phone on while holding down the Back key, which will do nothing special if the phone was merely asleep, but will display the HBOOT version within about a second if the phone was completely off.
From that screen, press Volume Up and then Power to turn the phone completely off again.
I don't think you can. I just did some tests and even the slightest press of the power button will turn it on if it is actually powered off. I didn't like the having to press the power button to 'wake' up the phone myself. Would prefer if you could hit the home button or similar as a long press.
On my Samsung Galaxy S I can use either the home or power button to 'unsleep' the handset.
You can install a custom lock screen application and use hadrware buttons like optical tracpad to wake up the phone. More info in the blog post.