On some handsets triggering with the power button require 10 presses instead of 5.

[jmatsushita]

On Samsung Galaxy S2, triggering the alarm requires 10 hardware power button presses instead of 5.

[jmatsushita]

With the proper timing of presses (between 1 and 2 presses per second but not faster) the alarm requires 6 presses currently.

[jmatsushita]

The number of required button presses is now 4 plus a confirmation press. With the proper timing as indicated in the image below, the number of presses required is correct.