We commit to each other out of love, pledging to recognize our partner as the only one with whom we will share our life. Yet, infidelity is all too common, and remaining faithful has become something truly rare and precious. People are not always able to restrain themselves or make the right choices, and that is how betrayal finds its way into relationships.

Marriage is one of the most important vows a person makes in a lifetime, and the weight of betrayal equals the weight of that vow. That’s why the presence of a third party in a relationship is so devastating.

At Yitong Investigation Agency, we help you understand whether your partner’s heart is still with you, how to recognize signs of infidelity, and how to protect yourself through evidence collection if your partner has already cheated.

What is the Definition of "Catching Adultery"?

In the past, adultery was defined under the criminal law as having sexual relations with someone other than one's spouse, which constituted a violation of marriage and family, and could be punished through public prosecution.

To collect evidence of adultery, investigators would gather proof at the very moment the act occurred, providing crucial evidence for court rulings — this practice is known as "catching adultery."

Although adultery has been decriminalized, collecting such evidence remains highly valuable, as it can serve as strong support in civil lawsuits.

What is the definition of “catching in the act” (adultery)?

In the past, Taiwan’s criminal law defined adultery under the “Crime of Adultery” statute, which allowed the state to prosecute individuals who engaged in sexual relations with someone else's spouse, under the “Crimes Against Marriage and Family” category.

To collect evidence of adultery, investigators would attempt to gather proof on the spot while the affair was happening, usually during sexual activity, to be used as court evidence — this is what we call “catching in the act.”

Although adultery has been decriminalized, gathering evidence of infidelity is still possible and remains powerful in civil lawsuits as proof for claiming compensation.

Who is more likely to cheat?

Based on the experience of detective agencies, we’ve identified six typical signs that a person might be cheating, which can help you detect suspicious behavior early and prevent heartbreak.

• Sudden concern for appearance

  In a long-term marriage, people often stop paying attention to how they dress, and the relationship can fall into a comfortable routine. However, if your spouse suddenly starts dressing up, applying makeup, buying new clothes, and putting effort into their appearance, it could indicate there’s someone new in their life they want to impress.

• Changes in daily routine

  If your partner, who used to work a steady 9-to-5 schedule, suddenly starts working overtime or making excuses to be away from home — especially on weekends — you should be cautious. This could be a cover for spending time with another man or woman.

• Frequent unexplained outings at night

  Sometimes, a third party will deliberately call when your spouse is with you, as a way of asserting dominance. Even if the cheating partner knows you’re nearby, they will still respond, often finding excuses to leave the room or go out. If this becomes a pattern, it’s a red flag.

• Decrease in sexual intimacy between husband and wife

  Whether it’s the husband or wife who’s cheating, the quality and frequency of sex at home often drop. It’s like having a meal — if they’ve already “eaten” elsewhere, they’ll have little appetite at home. If sexual relations become rushed and unsatisfactory without any reasonable explanation, infidelity might be the cause.

• Always carrying their mobile phone

  In today’s world, smartphones are the primary tool for communication — and for hiding affairs. If your partner suddenly becomes extremely protective of their phone, acts nervously when you pick it up, or you discover a second phone you didn’t know about, you should investigate further.

• Becoming secretive about finances

  Affairs often involve expenses — dates, gifts, hotel bills. If you notice unfamiliar spending or hidden withdrawals from your joint finances, your partner might be financially supporting another person.

How to catch a cheater? Hire a detective agency for evidence collection

Once a detective agency receives a request, they will carefully gather relevant clues — such as the specific changes in your partner’s behavior that triggered your suspicion. Investigators will then analyze whether these behaviors align with infidelity patterns.

If your partner is indeed cheating, they will inevitably need to carve out time for secret meetings, which will create changes in their daily routine and whereabouts. The agency will use surveillance and tracking devices to monitor their activities during suspicious timeframes. If the partner is observed meeting someone under questionable circumstances or entering potentially compromising locations, the agency will notify the client.

At that point, if infidelity is confirmed, the client can proceed with an on-site “catch in the act” operation.

• The Affair Partner’s Decline

  For example, if a woman is involved with a husband for money, revealing that she doesn’t truly love him but loves his wealth can make the husband realize that the affair partner is not as desirable as imagined, leading to the end of the affair.

• External Factors

  External factors can include geographical reasons or future plans, and the separation is not necessarily intentional. Common external factors include job relocations, assignments to different cities, or the affair being exposed to others, prompting the couple to break up or end the affair due to family or workplace concerns.

• Spouse’s Firm Opposition

  When the legal spouse takes a firm stand and tells the partner they must choose between the affair and the family, or face divorce, property division, and custody issues, most of the time, considering social perceptions and the children’s situation, the unfaithful spouse will choose to return to the family. This is the most common situation in which affairs end.

What evidence is required to sue for infringement of spousal rights?

Even after the decriminalization of adultery, you can still sue for civil compensation if your spouse has an affair. Although criminal punishment is no longer possible, civil law still offers protection for the injured party through compensation claims.

According to Article 184 of the Civil Code:

Anyone who intentionally or negligently unlawfully infringes on the rights of others shall be liable for damages. The same applies to anyone who intentionally causes harm through actions that violate good morals.

Article 195 of the Civil Code:

If a person unlawfully infringes on the body, health, reputation, freedom, credit, privacy, chastity, or other personality rights of another, and the circumstances are serious, the victim may claim compensation even if the damage is non-material. If reputation has been harmed, the victim may also request appropriate remedies for restoring their reputation.

Article 1052, Paragraph 1, Subparagraph 2 of the Civil Code:

If one spouse engages in consensual sexual intercourse with someone other than their partner, the other spouse has grounds to file for divorce.

Unlike the old adultery law, proving infringement of spousal rights does not require evidence of sexual intercourse. Acts that exceed normal social behavior between a man and woman — such as holding hands or kissing in public, checking into a hotel together, or sharing the same room overnight — could be enough to establish civil liability for violating spousal rights.

That said, while holding hands or kissing might suggest an affair, it is usually not strong enough for severe penalties in court. Without direct evidence such as “catching in the act,” the cheating partner might argue they were simply working or staying at the hotel for business reasons. That’s why on-site evidence collection is so important: it gives you leverage in court and increases your chances of securing a fair ruling.

What is the process for filing an infringement of spousal rights lawsuit?

Since infringement of spousal rights falls under civil law, police and prosecutors do not handle these cases. To pursue a lawsuit, you need to file a civil complaint either by yourself or through an attorney. The process is as follows:

• Step 1:The plaintiff files a lawsuit, specifying the parties involved and the nature of the dispute.
• Step 2:The court initiates mediation. If both parties refuse to attend or the mediation fails, the case proceeds to trial.
• Step 3:The plaintiff presents evidence. In spousal rights cases, this may include chat records (e.g., Line messages), video, audio, or witness testimony to prove emotional harm and infringement of marital rights.
• Step 4:Once sufficient evidence is submitted, both parties proceed to oral arguments in court. The judge will consider all the facts and evidence presented before making a ruling.
• Step 5:The court announces its verdict. If either party disagrees with the decision, they can file an appeal.

Why choose Yitong Detective Agency for infidelity investigations?

With nearly 40 years of experience, Yitong Detective Agency boasts the most professional investigation team and state-of-the-art equipment. We not only assist with catching cheating partners and collecting evidence, but also provide free legal consultations for future divorce proceedings and property distribution.

Moreover, Yitong cares about our clients’ emotional well-being. We offer free relationship counseling services to support you during this difficult time. Our primary concern isn’t profit — it’s about helping victims reclaim justice and ensuring that, once the legal battle is over, you can walk away with your dignity and peace of mind.