Detect When Tab has lost focus

[jmorlock]

We have a form with multiple tabs, and under one tab we have it programed to send messages through e-mail. We want to detect if there is data entered for the message but has not been sent. Is there some way to detect if they try leaving the message tab by either exiting out of the program or by clickin another tab. Some type of lost focus event would be ideal.

Thanks in advance,

Jeremy Morlock