It is easy to interpret your question in two distinctly different ways!

Did you mean:

(a) Is it likely that a person being surveilled (the subject) may become aware that they are under surveillance?

OR

(b) Is it possible that the surveillance operative (the surveillant) may themselves be under observation, by either the subject of the surveillance or their associates?

These are both very important facets of surveillance work and are significant pitfalls to the successful conclusion of any such operation.

The bottom line is that any surveillant cannot simply just become invisible, although it would be convenient. The art therefore is not to be noticed. There are many and varied ways in which to try to achieve this, which I would not disclose here for fear of putting operatives at risk. However common sense says that efforts made to change your physical and/or outward appearance can be very effective.

If you get a chance to watch that classic movie “The French Connection” with Gene Hackman as Popeye Doyle, you will notice that a significant part of the film is devoted to various aspects of surveillance work.

The old adage ‘Who is watching the watchers?’ is very apt and this is where counter-surveillance techniques can be employed to give you a chance to ascertain whether you are the watcher or the watched.

Strict operational guidelines, codes of practice and UK legislation exist to ensure that any such surveillance is conducted in as professional, ethical and non-intrusive a way as possible. So sleep well in your beds, unless you have something to hide?