It's called Zoombak, and it might be hidden in your briefcase right now.
A LoJack for the Facebook generation, all you have to do is text this pager-sized trifle and it'll text back the GPS coordinates for wherever it happens to be, meaning your map-savvy admirers will have no trouble finding out if you're gallivanting around downtown instead of putting a late night in at the office. Not that you'd ever do something like that...
The battery charge lasts five days—in other words, a long weekend—and it's light enough that you won't notice it in your overnight bag. Over that time, it can respond up to 150 times (depending on how intently you're being tracked), so whoever's checking in can put together a pretty detailed picture. The website even provides tracking software, complete with customizable zones and alerts to raise a red flag if you enter any troublesome areas.
For instance, the bathroom at the Beatrice Inn.