A cheating spouse is not going to leave evidence of his/her cheating out in the open. Most are sly and good at covering their tracks. So, where do you go if it is hard, cold evidence you are looking for?
You go where normally only the cheater goes. The cheaters territory, the place they feel most in control of is where you will find signs of cheating.
For instance, wallets and purses, they are great hiding places for phone numbers, notes from lovers and credit cards you may not know about with charges you aren't aware of. Look in hidden pockets or behind photos and credit cards.
Pockets can store a wealth of information about the person those pockets belong to. Look in coat, shirt and pants pockets for slips of paper you were never meant to see.
Gym bags, does your spouse visit the gym often? Stinky, smelly gym clothes are the last place they would expect you to look for such things as a second cell phone or receipt for a motel room.
You don't have to hire a detective or skulk around following your spouse if you have suspicions. More than likely you can find what you need in the comfort of your own home. The lists of places to look are many. Places like, computers, smart phones, home office desk drawers, golf bags, backpacks, CD cases, behind framed photos, the glove compartment of the car, under car seats, over sun visors and especially in the truck. Lots of hiding places in the trunk of a car!
If you feel the need to spy on a cheating spouse, start where they live.