I’m a private investigator who uncovers affairs – this is what gives people away

Paul Lewis is the founder and director of PEL Consultancy Services, one of the UK’s most established private investigation firms. With over two decades of operational experience, PEL has completed more than 4,500 investigations across corporate, personal, and international cases. If you suspect that your partner is being unfaithful, you may enlist the help of a private investigator (PI) to help gather evidence. PIs work independently from police and other law enforcement agencies and work on matters such as infidelity, background checks, surveillance, fraud, and employee dishonesty. Surveillance may be physical, like tracking someone’s movements, or involve investigating their digital footprint. Here, PI Paul Lewis explains what he’s learned about affairs from decades on the job, how technology has changed his role, and what motivates people to cheat. Shorts There are seasonal peaks in affair investigations Affairs investigations make up a significant proportion of our personal cases. It varies by season, with peaks around January (which is widely known as “Divorce Month”) and after the summer holidays, but at any given time we will have several running simultaneously. What surprises people is how often the client already knows the answer before they call us. They are mostly looking for confirmation, not discovery. The biggest red flags to look out for Behavioural change is almost always the starting point when it comes to someone concealing an affair. Sudden interest in their appearance, unexplained absences with vague explanations, a phone that never leaves their hand and is always face down, irritability at home combined with unusual cheerfulness, and a new person mentioned slightly too casually and then never again. The last one is particularly telling, as people having affairs often reference the other person once to establish normality and then deliberately avoid the name entirely afterwards. Some suspicious behaviours are not always what you think Working late is probably the most common trigger for suspicion that turns out to be exactly what it appears. Financial secrecy is another one. Most people assume that being cagey about money is a sign someone is cheating, but we have investigated cases where a partner was hiding significant expenditure because they were planning a proposal or a surprise holiday, not because they were funding a second relationship. Stress changes people’s behaviour in ways that can look suspicious but are entirely unrelated to infidelity. Technology has changed how PIs work The volume of requests to investigate affairs has stayed consistent, but how investigations are carried out has changed considerably. Ten years ago, the majority of cases involved straightforward physical surveillance. Today, a significant proportion have a digital dimension from the outset. Encrypted messaging apps, multiple phones, and social media accounts under assumed names have all become standard features of cases that would once have been far simpler. The emotional stakes have not changed at all, but the methods have changed enormously. How people cover their tracks The increase in the popularity of AI has brought both more opportunities and new challenges to our work. AI has given investigators better tools for pattern analysis and intelligence-gathering, but it has also given people having affairs better tools to manage their deception. Catching someone using encrypted messaging apps like Signal, WhatsApp or Telegram relies less on breaking the encryption (which is nearly impossible) and more on observing behavioural shifts, spotting physical device habits, or finding hidden app interfaces. The vulnerability is rarely the software – it is the human routine. Most affairs start in the workplace The term work husband or wife is often used in a jokey way, but close working relationships are still the most common way for affairs to start. This is mainly because of the amount of time people spend at work and the intensity of shared experience. Old flames reconnecting through social media have become a much more significant category over the past decade, as Facebook and Instagram have made it extremely easy to reopen doors that would once have stayed closed. Online connections that begin as something else – gaming communities, professional networks, hobby groups – have also become increasingly common places where infidelity starts. The motivation for cheating is rarely just sex Despite what many partners think, affairs are almost never purely physical. The cases we see most often involve someone who feels invisible at home, who has stopped being seen as a person rather than a function. The affair fills a gap that neither partner has had the conversation to acknowledge. But that does not make it any less painful for the person on the receiving end of our report. Most cheaters assume they’ll never get caught I find the confidence and arrogance of cheaters who think they’ll never be found out staggering. People believe that if the messages cannot be read, there is no evidence. What they underestimate is that behaviour leaves a trace that technology cannot erase. The pattern of absence, the change in dynamic at home, the financial irregularities. These are all things a trained investigator notices long before digital evidence becomes relevant. Breaking the news to a client never gets easier Revealing infidelity never becomes routine. The client almost always knows what we are about to say before we say it. There is a particular stillness that settles in the room at that moment. Some clients cry. Some become very calm and practical. A few express relief that they were not imagining it. But it never gets easier.