Juice Defender disables data connectivity and re-enables it after certain interval to save battery and can increase the life of the battery by 2-3 times.
Lookout Security app is a much because it acts as a virtual guard and can help you to locate the phone if it is really lost. The problem is that if you are running this app with Juice Defender, then you data is disabled and you can not locate the phone.
This is where a hidden feature in Juice Defender comes really handy. There is a feature to define a password that you can send to your phone and Juice Defender would disable itself.
With the combination of these two applications, you can save battery as well as secure your android device.