There are a few signs - working late more often, more and more "girl's nights out" when you want to get together, strange text messages from new "friends" - that can trigger paranoia that your girl is engaging in a little extra-curricular activity behind your back.

So how do you find out for sure? You can't ask her friends. They'd sooner broadcast their actual weight, than what you're girl's been up to. You'll have to do a little recon work of your own, so here are a few tools you can use to find out what she's been up to.

[Note: Is it ethical to spy on your girl? That's a gray area. If she is cheating, then you can justify invading her privacy. If she's not, you'll have to live with being a jealous loser forever. And make sure to check local laws too. Some forms of "information gathering" may be illegal. Living as a jealous loser may be tough. Living as a jealous loser who's locked up is tougher.]

Smile. You're on Hidden Camera.
You can thank bad nannies for these handy cams. Sites like SelfDefenseProducts.com carry an entire house-full of ordinary-looking, everyday objects like an alarm clock, book, desk lamp and flower pot, that come equipped with hidden cameras.

You can record the evidence to your laptop with the DVR Guardian ($99), a four-channel USB surveillance system that handles up to 4 cameras. It'll also let you set recording times, work off of motion detection, and monitor what's on the cams from your cell phone. (Your mission, however, is to figure out a way to get all this stuff into position.)

GPS Snitch.
This handy little device was actually designed for locating a stolen vehicle, but in the hands of a jealous guy, it becomes a stalker's best friend. By combining high-sensitivity GPS technology with the wireless data capabilities of cell phones, GPS Snitch provides real-time location tracking over the internet. It's completely self-contained, requires no installation, and is small enough to be hidden in any car. Once it senses movement, the Snitch sends a text message to your phone, and you can track it through their website. ($399, plus monthly service for the tracking service. Small price to pay for peace of mind of knowing if your car, or girl, is stolen.)

Grab a Cap.
Used by offices to make sure you're not using company resources to download this weekend's porn, inexpensive screen capture software from companies like SpectorSoft can record where she's been online, her emails, IMs, Myspace chats, photos she's looked at... anything and everything she's doing while in front of the screen. All without her knowing, and all for you to look at later. Makes having to guess her password obsolete.

Take a REALationship Quiz.
If there's one good thing about Cosmo magazine, it's that it has socialized women to react like Pavlov's dogs to relationship quizes. "Are you Compatible?", "Will Your Relationship Last?", "Is He Husband Material?"... it's like quiz-crack to women. And over at REALationship.com, they're exploiting that fact to your advantage. You can send any number of their quizzes to your girlfriend's email, MySpace, Facebook, etc., just like she gets all week long from her friends. The only difference with a REALationship.com quiz is her answers are sent directly to you. Just make sure you really want to know the answers before you sign up.

Bottom line is there are any number of ways in this information age to find out what she's doing and where she's doing it. It's just a matter of should you take advantage of this technology, and are you man enough to handle the truth?