How To Password Protect iPhone/iPad Apps Using Lockdown Cydia App
If your kid borrows your iPhone or iPad for watching your family video, you certainly wouldn’t want him to get access to social networking apps such as Twitter, Facebook or an IM client such as Fring or Yahoo Messenger. Lockdown is a free jailbreak app for iPhone and iPad that lets you set a password for any iPhone or iPad app.
Here is how you can password protect your iPhone or iPad apps using Lockdown:
1. Jailbreak your iPhone or iPad and install Cydia.
2. Launch Cydia, and tap on ‘Sections’ at the bottom of the screen.
3. Scroll down the list to find ‘System’. Select it to view all the available packages .
4. Select ‘Lockdown’ from the list of packages. In case you are unable to find Lockdown, make sure you have added Big Boss repository to your Cydia sources.
5. Download and install Lockdown, which is currently available free of cost. 
6. After the installation is complete, restart your iPhone or iPad Springboard. You will find Lockdown as one of the apps. Launch the app.
7. You will be required to give a safety word, and a password. Confirm the password and hit Continue to go ahead.
8. Lockdown scans your iPhone or iPad and shows up a list of all installed applications. Select an app, and you will be asked if you like to lock down the application. Select ‘Lock’ to restrict it’s access to any other users of your iDevice.
That’s it. The next time an application is opened, Lockdown will first prompt for password. A small irritation that you have to put up with such a good security is that you will have to input the password each time you open a protected application.
It don’t work on iPad ;-(
Do you know one app that work on iPad?
I need to be able to password the Contact app.
madvlock is expensive but works great on ipad.
oops, actually it seems madvlock doesn’t have an option to lock the contacts app. BUT if you use categories you can put your contacts in a folder and lock at. also, madvlock has a free trial period.