When using surveillance detection principles as part of your personal security program there are two levels that can be used: passive and active. In an active program you would design an implement surveillance detection routes (SDR) that include preplanned stops and movements designed to cause anyone that might be following you to inadvertently expose themselves. This requires a level of training and practice and is probably not necessary for most people most of the time.
The second method is passive surveillance detection which can be done very simply. It does require a level of focus and awareness but with a little practice this can become a habit.
Three of the key components to watch for are:
Time and Distance: Seeing the same person, people or vehicles over time and distance. For example if you see the same person at the airport, then later at you hotel and then at the restaurant where you are having dinner it could be simply coincidence or it could be a cause for concern. The greater the frequency and the greater the number of sightings the higher the level of concern that you might be under observation.
Correlating Actions: Watch for people and vehicles whose movement appears to correlate with yours. An example would be when departing your house you pull out into the street in your vehicle and a car that has been parked up the street pulls out into traffic behind you. Things to watch for are: people who either move or seem to take notice when you move or arrive/depart at a location.
Out of place: Watch for people whose appearance and or behavior appears incongruous with the environment they are in.
With the exception of national intelligence and security services and some sophisticated terrorist organizations most surveillants are going to have a very rudimentary skillset and limited resources. When they succeed more often then not it’s because many if not most people walk around all day in a fugue state. Understanding these simple principles, applying them and being alert will go a long way to keeping you safer.