A good source of information on ethics in private investigations is the Association of British Investigators (ABI) guidance. Operant Investigators Ltd have high standards of ethical practice in their work and so abide by the ABI's code of conduct.
Static cameras and monitoring certain areas using CCTV are again highly specific to your area. Licensing may be needed such as for the UK an SIA license is required under law however if your recording using a mobile, camcorder or other devices this is fine. As such it is something most PI's can do but with some caveats. If your placing a static device on private property facing at or towards private property then this should be fine as long as the person's being recorded couldn't reasonably expect privacy i.e. areas that can be seen from the road or another residence.
Wiretapping and phone monitoring cannot be done by private investigators under the cast majority of circumstances. Recording a phone conversation can be done with 1 parties or consent or just by informing the other party but like most things mentioned on this post it is dependant on the local laws again. Some countries and states require 2 party consent.
There are a variety of tactics and techniques private investigators can employ they are continuously evolving. As such it is impossible to mention everything a PI can and cannot do. In the UK a PI can do everything a private citizen can and is afforded no additional rights or access. This is different in the US and some countries however generally speaking a PI can do everything a citizen can under the local laws. They usually have greater knowledge, access and critical thinking abilities which is what you pay for.
Proportionality, reasonable expectations of privacy, legitimate interests and ethics should be thought about and discussed prior to work being completed. Following a small set of guidelines and principles along with the expertise of a private investigator should ensure compliance.
Operant Investigators Ltd - Private Investigators
Head Office in London, branches also in Bournemouth, Bridgend, Southampton and Taunton.
Registered at 71–75 Shelton Street, Covent Garden, London, WC2H 9JQ