From Jarrod Ribble:
Two Key On Hack is a HackMaster hack for PalmOS that makes it so your Palm will only turn on when the contrast button is pressed. This is a very simple way to overcome the problem of your Palm V turning on in your pocket. Please note that if you install and activate this hack on a Palm device without a contrast button you will not be able to turn the Palm back on. You will have to do a reset and tell HackMaster not to reactivate the hacks.
A known problem with this hack is that if you set an alarm, your alm will not be able to turn on and beep when the alarm goes off. You won't get the alarm until you turn the Palm on by hand. I don't use alarms, so I didn't worry about figuring out how to fix this.
Please note that this software is licensed under the LGPL. You are welcome to use it for your own purposes. If you come up with something cool, let me know!