You can use the InTheHand.WindowsMobile.Forms.MobileDevice.LockAndPrompt() method to put the device into a locked state using the PIN/ alphabetic password which is set on the device. If you want to lock access to just your application you can do this anyway you choose e.g. by creating an initial login screen and securely checking the entered pin/password - make sure any data you store with your app cannot be accessed outside of your app. For example use encryption with your database. Using the LockAndPrompt method is easier because it will lock the whole phone but you need to ensure the device has a password setup. Depending on your Exchange server settings you can enforce a security policy which requires the device to use a password.