Cosmopolitan reports that some people are adding an affair partner as a collaborator on a shared note in their phone’s Notes app, just to send hidden messages their partners “wouldn’t suspect or think to check.”

Queensland private investigator Cassie Crofts described the same trick to Nine.com.au: messages are written, read and deleted, so “there’s no trace of what’s going on.” Tellingly, Crofts also said she “wouldn’t recommend snooping” through your partner’s phone.

It joins a long list of phone tricks Cosmo mentions, like saving someone’s number as “Pizza Hut,” disguising a contact as a five-digit number so it looks like the bank is texting, or using secret messaging apps. The app is just the hiding place. The behavior around it is what you’ll actually notice.

None of these is proof on its own. People change for all sorts of innocent reasons. What matters is a cluster of changes, especially paired with new secrecy. Men cheat, women cheat; as Crofts puts it, “everyone has the potential,” so these signs apply to any partner.

1. He suddenly takes much better care of himself

A new gym habit or nicer clothes can simply be self-improvement. It’s worth noticing when it comes with secrecy, or when it doesn’t seem to be for you. Crofts gives a very specific example: a car that’s usually “a toxic dump of old coffee cups” is suddenly spotless, often because someone is getting picked up or impressed.

2. He has sudden new tastes and hobbies

Crofts says a big change in hobbies or music taste can sometimes be a sign: “If you used to have to drag them to the beach, and suddenly, they’re surfing … every weekend, it’s a bit unusual.” New interests are healthy. New interests he won’t talk about, or that always seem to involve the same new person, are different.

3. He spends a lot less time with you

Missing date night once in a while is life. If he suddenly avoids time alone with you, or his free hours keep disappearing without explanation, something has shifted.

4. He has new friends you haven’t met

If he keeps mentioning people he’s never brought up before, but you never get to meet them, pay attention to how he reacts when you ask.

5. There’s new secrecy around his phone

This is where the modern tricks show up. Crofts lists changing passwords as a phone-related sign, and Cosmo mentions renamed contacts, secret messaging apps and shared notes. More everyday clues: the phone is always face down, it goes to the bathroom with him, or he gets jumpy when it buzzes. Notice the change from his normal, not just the habit itself.

6. He treats you differently

He’s distant, on edge or more critical than usual. Stress at work can do this too, so look at how long it lasts and whether he’s willing to talk about it.

7. He accuses you of cheating

If he was never the jealous type but suddenly treats you with suspicion, it can be a sign that something is going on with him. Treat this as a pattern some people notice, not a rule; plenty of jealousy comes from insecurity, not guilt.

8. His friends and family start acting differently around you

Crofts says friends “acting different around you” can be a red flag: “If they’re not meeting your eye, not engaging as much, it might be because they know something is going on.”

9. There are money moves you can’t account for

Crofts notes that when someone who normally pays by card or phone suddenly uses cash a lot, it can be because they’re buying things or booking hotel rooms they don’t want showing up on a joint account. Hidden spending can also be its own problem; read more on financial infidelity.

10. His story keeps changing

As Cosmo points out, partners pick up on changed behavior even when they don’t know the details: more time on the phone, feeling disconnected, stories that start to sound inconsistent. If the explanations keep shifting, trust that you noticed.

Therapists who spoke to Cosmopolitan offered a few reasons:

That’s why people can cheat even when they say they’re happy. Cosmo notes that some people love their partner and still seek connection elsewhere. It isn’t always a verdict on you or your relationship.

Yes, and it’s worth sitting with that before you act. Crofts told Nine that people who’ve been cheated on before are more likely to wrongly suspect a new partner. She described one case where a client was sure her partner was cheating. Surveillance showed his unexplained absences were visits to his very sick mother, who had just moved into a nursing home.

One sign alone isn’t proof. Look for clusters of changes from his usual behavior, over time. And if you’ve been hurt before, be gentle with yourself; your alarm system may just be working overtime.

The short answer: no. Even the private investigator says she wouldn’t recommend snooping. Going through someone’s phone or accounts without permission can damage trust whatever you find, and depending on where you live, it may carry legal risk too.

It also doesn’t fix the real problem. If you feel you need to check, the relationship already has a trust issue worth talking about directly.

Try naming what you’ve noticed instead:

“I’ve noticed you’ve been on your phone a lot and kind of far away lately. I’m feeling uneasy. Can we talk about what’s going on?”

Pick a calm, private moment. Talk about the changes you’ve seen and how you feel, rather than leading with accusations. Then listen to the answer, and watch whether the behavior changes.

If you feel unsafe: if your partner is controlling, threatening or monitoring you, or you’re afraid of how they’ll react, reach out for support. In the US, the National Domestic Violence Hotline is available 24/7 at 1-800-799-7233, or text START to 88788.

What is Notes-app cheating?

It’s when someone shares a note in their phone’s Notes app with an affair partner and uses it to send hidden messages, often deleting them after reading so there’s no trace.

Can someone cheat even if they’re happy in the relationship?

Yes. Therapists who spoke to Cosmopolitan say some people cheat to avoid dealing with problems, some want both security and excitement, and for some the secrecy itself is part of the thrill.

Should I go through my partner’s phone?

It’s not recommended. Even the private investigator quoted by Nine.com.au says she wouldn’t recommend snooping. Accessing someone’s phone or accounts without permission can harm trust and may carry legal risk. Talking about the changes you’ve noticed is a better first step.

How do I bring up suspected cheating?

Choose a calm, private moment, describe the specific changes you’ve noticed and how they make you feel, and ask an open question, such as “Can we talk about what’s going on?” Avoid leading with accusations.

Could I be wrong about the signs?

Yes. One sign alone isn’t proof, and people who’ve been cheated on before are more likely to wrongly suspect a new partner, according to the private investigator. Look for a cluster of changes over time.