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The phone is a common thread in all our lives, and it's only becoming more so as time goes on. So it is a pretty sure bet that their Affair d'amour is happening over the wires as well as—well, you can imagine. Phone sleuthing is easy.  Take a spare to somewhere in the house where he/she rarely goes, and plug it into the phone jack. Unscrew and remove the mouthpiece (ahead of time) so that your sotto voce epithets will not give your sleuthing away. When you hear him/her shout "I've got it, honey" (cause you just know it's him/her), go to your "war room," and very carefully lift the receiver off the hook. Don't be too gentle: wiggling the buttons will make a clickety sound on the line that will get you busted. If you're pretty sure your soon-to-be-ex-honey is not going to call up his/her burning biscuit of bliss while you're around, but that he/she may not be able to resist a little sneaky call when he/she thinks you're not looking—or his/her cohort in canoodling may just have to hear his/her lover's voice before he/she goes to bed with "him/her", recording the conversation might work. If you plan ahead, you can tap the airwaves as he/she taps his/her inner Don Juan. If you have a smart phone or a feature phone with a recorder, set the earpiece of the headset next to the microphone, and record the lovey-dovey ramblings for posterity. If the jig is up, and you have what you need, then no need to wait. Confront the louse with his/her toothbrush and an overnight bag, and send him/her out without his/her dessert. If it turns out, however, that the phone was his/her bowling buddy confirming Lane 6 this Thursday, whip up his/her favorite dessert, and serve it up with a smile. This is the cheap, low-tech way of listening in. Of course, if there are no babies in your life at the moment, this can be a bit tricky, but you can get around that. Wait till he/she goes out "shopping" one day, and hit the local gizmo shop. Get a basic baby monitor, a can of spray paint that will blend with where you will put the transmitter, and a roll of matching masking tape (in case the transmitter has blinking LEDs on it).  Paint the transmitter (the baby/secret side) with the spray paint. Cover up the microphone hole before you paint so you don't gum up the works, and don't over-paint. You don't want that thing to be stinking up the house. Go to the room where you think she'll be making throaty sounds with her licentious Lothario, and cache the transmitter in a discrete location where she's unlikely to look. Behind some books, or the couch, or if you're really hapless, somewhere in the bedroom or bath. Power it up, and put a portable radio in the room turned down to about human-whisper-and-giggle level. Go into your man cave, and turn on the receiver. Can you hear the radio? If so, you're ready to go. If not, make adjustments until you can hear the transmitter signal clearly. When that phone call comes, and she says "I have to get this... it's work," say, "Okay, honey, I'll be in the man cave surfing the 'Net for..." (You can say almost anything there: after she hears Okay, honey, I'll be..., she'll already have too much adrenaline pumping through her to hear you, anyway.) Go to your room, turn on the monitor, power up your recorder (phone, tape, whatever you've got), and listen to what happens next. Should you hear what you fear, call her a taxi, and send Ruby Roundheels on a one-way ticket to town. Of course, if you hear "Okay, I'll have that report by tomorrow, boss, and I.... wait, what's this... a transmitter?," you might want to take that taxi yourself. You're going to be in hot water. There is a range of digital records, from pens, or thumb drives, or even phone look-alikes that are voice activated. That means you can just set one wherever you think your spouse may go for his or her phone fun, and when it happens, the electrical spy will spring into action, like a steel trap. Check that trap at your convenience, and good luck! Direct access of your cheating cherie's phone can reveal a lot—especially texts and tweets. Her close friends will be quite frank with advice and what they think. You may find the texts that are sent give you more insight than the ones received. A regular check will give you an idea of how things are progressing. Watch out for the use of false names so that if an incoming message arrives at an awkward moment, the false name gives nothing away.  Check email. Another way he'll schedule snogging sessions with that woman is to send send her emails or chat online. What if every email or conversation that your spouse sends online got mailed to you to read? Software called remote spy software records all of his or her emails, chats, instant messages, web sites visited and keystrokes and then automatically copies this recorded information to your email address. Unless your spouse is very careful, you can also pop onto his or her computer (or phone) when he or she is not around, and look at history, recent applications, and other breadcrumbs to follow the trail of the philandering fink. Maybe a little email planning for the next rendezvous with romance, or some online hot chat logs. The lout who is having the affair will quickly try to prevent you seeing emails through the use of passwords and saving the emails under different file names. To gain access initially, you may try using his typical passwords as a starting point. If that doesn't work, a Google search will easily find specialized software that can hack passwords.
Let your fingers do the walking. Perform some phone sleuthing, if you have a good old-fashioned land line. Press Record Now. Use a baby monitor. Record digitally with a digital recorder. Break all trust and spy on your honey's personal communications.