When armed and iAlertU triggers movement, the alarm works, but the sound stops when lid is closed immediately afterwards. iAlertU works perfectly in open-lid conditions, but when the lid is closed, the sound stops immediately.
There is nothing more that we can do about this. Macbooks, by design, go into "clamshell" mode when the lid is closed, and as such the application loses the ability to send email, sound the alarm, etc.
This is why I added the features that will allow you to configure the application to arm or trigger when the lid is reopened. If the thief closes the lid, yes the sound will stop shortly after as the operating system stops iAlertU from doing everything (it goes to sleep). When the lid reopens, the app can re-arm and even trigger, thus hopefully sending out information about when the macbook has been taken to, and maybe even an image of the thief when s/he is reopening the lid.
Unless Apple have changed things in Lion to allow iAlertU to run in clamshell mode (and I doubt it), there's nothing I can do.