My top pick for tips on how to catch cheating is this book by Sarah Paul

How You Can Catch A Cheating Spouse

When you suspect your spouse is cheating on you, there are ways you can go about finding out if this is true without engaging the services of a private investigator. You do have to be careful not to arouse the suspicions of the cheating spouse because this will only make him/her more careful or even angry if it is not the case. You may feel a bit guilty about taking devious steps to spy on your spouse, but it is necessary to alleviate your suspicions.

First of all, you should be aware of the callers to your home phone. If you notice that the list is always empty where it was once your job to check the calls and erase the numbers, this is something that will arouse your suspicions. If your spouse has a cell phone, you can devise a situation where you can check the callers on this phone and take note of any number that seems to be calling a lot or that your spouse has been calling. Using a reverse phone look up, you can find the name of this caller and the address. This is easy to do with a landline and there are free online services that will help you learn who the caller is. With cell phones, it is harder to get this information through a free service, but the cost involved is not very high. This is something you can do from home without anyone knowing anything about it.

You can also record your spouse’s side of the conversation when on the cell phone in the car. There are digital recording devices that you can easily install under the dash, under the seat or even in the trunk, as long as the microphone is in the car itself. Your spouse will never know it is there. It does not beep or have a signal light and will only come on when activated by a noise, such as a voice or the ring of a cell phone. Although you may not learn the full name of the person with whom your spouse is having an affair, you will hear enough of the conversations to confirm your suspicions. You do have to be careful if this is the step you take because you may hear unflattering comments about yourself.

Another step you can take is to follow your spouse and see where he/she is going. For example, if there seem to be a lot of evening meetings all of a sudden, you can discretely follow to see if the meeting is actually at the office or at a restaurant or even a hotel. When your spouse says that he/she has a dinner meeting, you can casually ask the name of the restaurant. If there is hesitation or questions about why you want to know that, you can assume that there is something else besides a business meeting occurring. If you do learn the name of the restaurant, you can drive by to see if your spouse’s vehicle is in the parking lot or even sneakily check in the restaurant, itself, to see whom he/she is dining with. This last action is very risky though, as you run the chance of getting caught spying.