There is no harm in letting the person you are following know that he is being monitored through the surveillance device. Allow him/her to see you "accidentally" in the entrance hall of his company, at a regional bar or in your local food market. This type of obvious surveillance technique can be quite efficient in making the person look weird and may even help you in avoiding the risk of undesirable action.
Set up little surveillance cameras in places that are usually ignored by the concerned person. Places such as the check out area can be easily overlooked. Hide a camera behind something like bookcases, clothing, smoke detector, on the inside of the window etc so it cannot be seen by the person under surveillance.
Most modern day cameras are very small and can be easily hidden behind every day objects. The images captured by the web cam can be seen live.
Connect a little GPS monitoring system to the dubious person you want to look at. The monitoring system can give you a record of all movements and activities of that person.
You can also use a real-time monitoring system which can be very easily followed online on the product’s official website.
Always install the components of surveillance devices on your personal computer (well secured) as this will help you keep a record of all the information taken from the camera, without risking the leakage of information. If that is not possible, use a laptop, but be sure that the information on it is encrypted.
Equip yourself with things like a pen, a notebook and a personal diary. This will help your write down important notes, telephone numbers, contacts and address when you are on the road.