Wait? They can watch me?
In a personal injury case, it is not uncommon for insurers to conduct surveillance on you. You may think that you are entitled to privacy but, once you are in the open, the insurer can have an investigator follow you to see what you are doing.
The basis for surveillance is, in my experience, two-fold. The first is that it is to discredit an injured party by showing that they are able to do things that they allege they cannot do. This is when surveillance is used to impeach the credibility of the injured party. During my days practicing for the defense, there was a Plaintiff who stated that she could not do any gardening at home or at all. However, surveillance video showed her gardening at her local church despite her evidence and the evidence she conveyed to her doctors. As a result, her credibility was impacted adversely.
The other basis for surveillance is to show, even if you are not doing anything you say you cannot do, a trier of fact that you may be far more active than you are letting on. The surveillance is essentially used for the truth of its contents meaning that the surveillance shows that you are active and not as limited in your activities as you suggest.
An investigator may also perform background searches. As well, given the explosion of social media, the investigator (and counsel for the defense) may be able to access your public social media sites to see what you are doing and if you are doing anything that you say you cannot do.