Lidpop does two very simple things: It plays a sound of your choosing when you close your laptop's lid (or, more precisely, when your computer--laptop or desktop--goes to sleep), and it plays another sound of your choosing when you open your laptop's lid (when your computer wakes up). For example, if you're a sci-fi geek--not that anyone at Macworld would know anything about that--you could configure LidPop to play C3PO saying "How rude!" when you close your MacBook Air, and saying "Wake up!" when you open it. Or a...um...normal person might use the sound of a door slamming or tires screeching for sleep/shut, and a clip of a rooster crowing or a yawn for wake/open.

Lidpop provides 15 built-in sounds, but you can also use your own sound files. In my testing, Lidpop supports sound files in AIFF, WAV, MP3, and AAC formats (though only .m4a files--.MP4 and .m4v files didn't work).

Sure, it's a bit silly, but it's good fun that takes me back to the days of for System 7. And as I've been using it over the past month or so, it's regularly produced smiles and comments from passersby.

That said, Lidpop does make itself useful in certain circumstances. For example, if you've ever opened your bag to discover that your MacBook has at some point woken up--leaving you with a partially drained battery and an overheating laptop--you'll appreciate that Lidpop's wake-up sound can alert you to such inadvertent wakes. Just make sure you don't mute your laptop before putting it to sleep.

Which leads me to one of the features I'd like to see in Lidpop: an option to set independent volume levels for the wake and sleep sounds, unaffected by the system-volume level, so your sounds are audible even if the system volume is muted. I also wish Lidpop operated as a System Preferences pane, rather than as a menu-bar app--I've already got enough icons in my menu bar. (The developer that Apple doesn't allow preference panes on the Mac App Store. As a workaround, you can choose to hide the menu-bar icon, but then you must relaunch the app whenever you need to access its preferences.) Finally, it would be great if Lidpop's menus for choosing a sound automatically displayed any sounds in /Library/Sounds and ~/Library/Sounds, rather than making you navigate through an Open dialog each time you want to choose a custom sound.