* It's not exactly thrilling sitting all night in your car checking on someone who says his recent accident means he is house-bound, while the insurance company suspects the claimant is still running a night-time taxi business from home. A colleague who specializes in this type of investigation says that, instead of sitting up all night waiting to see if the person is working nights on the taxis, he places a small coin on the top of the rear tyre of the car, then goes home to bed. If the coin is still there in the morning, the car hasn't been moved all night. If it is not, it could have been blown off or knocked out of place, or the car might have been out picking up passengers. Either way, the investigator does a thorough surveillance job the night after any such movement occurs.



* Another investigator says watching for bedroom lights to go on and off in cases of suspected infidelity is the most boring part of his job. But he's found an easy solution to the problem. He sets his video camera to film for a couple of hours while he sleeps. An alarm clock alerts him when the video cassette needs changing. This he does, then promptly goes back to sleep!

* Stationary surveillance -- Sometimes an investigator needs to have constant access to his subject, perhaps watching that person or item over several months. This obviously increases the risk of being spotted. To avoid this, you may need to use rented rooms, rooftop vantage points, and other places that allow you to see but not be seen. Where you are working at some distance from your subject, binoculars, cameras and high-tech listening devices are essential. Where suitable vantage points are unavailable, as with most short-term surveillance, you might use sunglasses or a newspaper, or some other means of making yourself less obvious. A colleague says his best disguise is sunglasses with mirrors on the side, meaning he can still watch his subject while facing the opposite way.

* Surveillance on foot -- Long periods of tailing a subject don't work as well as in the movies, especially in open areas such as quiet streets and parks. It's easier in busy towns and cities, but here you risk losing your subject in the crowd. Get too close and you'll be spotted; walk too far behind and you'll lose them. Working as a team is a good idea for important jobs where the expense can be justified. Even in quiet places, three or four investigators can take turns to tail a subject, making discovery much less likely.

* Surveillance in vehicles -- Again, one car following another too closely gets noticed; but if you stay too far behind you'll lose the vehicle you are tailing. If you are tailing a walking subject, one person following by car is unlikely to produce results. Three investigators in separate cars, each taking over where one leaves off, can work wonders. For night-time work it is a good idea if possible to attach some form of reflective device to the back of the subject's vehicle: perhaps a strip or tiny sticker, which the subject is unlikely to spot. This will make the vehicle easier to recognize in the dark. Be careful when doing this, however, or you could damage the subject's vehicle and end up in court on a charge of wilful damage.

* Learn what you can from television and film detectives. These shows are carefully researched, often aided by expert consultants. Some useful tips can be gained this way.

* Double-check your photographic and recording equipment before starting a long surveillance task.

* Don't drink on the job. Excess alcohol lowers the concentration, distorts perceptions, makes you look foolish, reduces your credibility, and means frequent trips to the toilet!

* Don't assume all surveillance is undercover. Some investigators actually want the subject to see them, as sometimes happens in supermarkets where the store detective's obvious presence is to deter crime, not (primarily) to detect it. 'Prevention is better than cure' is the relevant maxim. A colleague who works in this field says he often makes his presence known in the hope of confusing the subject, perhaps causing that person to act in a rash way and make mistakes.

* A single car can be made to look very different by using the headlights for a period, then changing to fog lights, and alternating at regular intervals. But don't do this too regularly, in case the technique actually draws the attention you seek to avoid.

* Investigators in quiet areas like villages and parks will find a dog a useful ally. After all, a man out walking his dog can retrace his route, walk off the beaten track, and stop and stand still for a couple of minutes, without making anyone curious.

* The successful investigator never looks his subject in the eye; not for long periods, that is. Sunglasses -- even if they are a bit of a cliché in detective movies -- are a good idea in appropriate places and at particular times, as they mean you can look without giving the game away. At night or in the middle of winter, however, they are certain to attract suspicion!

* On a similar theme, never point your car directly at a subject. Park facing the other way, and watch your subject through the rear-view mirrors.

* Finally, be patient. 'Softly, softly, catchee monkey' Charlie Chan advised. And a large American detective agency adds to its promotional literature: 'We do nothing quickly'.