in Windows API ::
If you really want to grab the user attention and stop him from doing anything else, you need to be able to display a system-modal topmost message box even when your application is not active. Here's how when using Delphi.
If you really want to grab the user attention and stop him from doing anything else, you need to be able to display a system-modal topmost message box even when your application is not active. Here's how when using Delphi.
Read the full article to learn how to Display a TopMost System Modal Message Box (from an Inactive Delphi Application)
Related:

Hello,
This is very usefull for us, but does it also work for active windows?
Thank you
Veerle,
Yes it does
As it might be useful when you definitly want to draw user atention it can be very anoying in some circumstances. I might even cause a system crach. Wel not on its own, but by forcing some other aplication into certain circumstances when it becomes unstable.
What I’m talking here are computer games. Even nowadays most of them still doesn’t handle well when they are minimized or when they lose focus. Unfortunatly most computer games programers still thinks that when someone is playing their games they doesn’t do anything else. But since nowadays computer are very powerful it is more and more often that users keep some programs runing in the background even when they are playing computer games. And when one of those programs tries to draw user atention in the way wich is described in this article it might cuse that game to crash. And in some cases that game can then even cuse a operating system to freeze (quite comon on Win98 and prior, a bit rare on WinXP, but I haven’t encountered this on Windows7 yet).
So I advise some caution becouse your users would be very angry if your program would be the one wich would in the end lead to a potential data loos. Also most users don’t want to be disturbed while playing games, watching movies, etc.
@Silver Warrior: An example is the free version of “AntiVir”. It pops up a dialog and while doing stopping everything you are doing. Most programs wouldn´t crash but its very annoying.
“Stealing” the focus is not a good idea. While typing on something like word, you could even close that dialog without seeing it (pressing Enter for a new line) and after that all following keys are not in your document.
Maybe, a baloon or something like that would be a better solution.
Yes I completly agree with Arnd. Creating a balon help notification is a good idea. The advantages are that it is alway displayed above other alications except when you are in full scren mode. Also it is you hwo actualy controll wheter you want the baloon help message to autohide after certain times or is displayed until user closes it.
Also one of very powerful fetures od notifying user of some importain events is the use of system sound. This sound will be heard no mather what the user is doing (listening to the music, playing games, etc.) unles the users either don’t have speakers conected or has them turned off.