Guidance is being issued about the use of hidden cameras to monitor the care of people in hospitals and care homes.
The Care Quality Commission has produced a pamphlet that sets out what relatives in England need to consider.
It includes advice on gaining permission from the person being cared for and where it can be done.
The CQC said opinion was divided about hidden cameras but it was publishing the guidance in recognition of the fact some people were already using them.
It also comes after the BBC's Panorama programme used secret filming to uncover abuse.
This includes a programme in 2011 that exposed abuse at Winterbourne View, a residential hospital near Bristol for people with learning disabilities, and last year's expose of the Old Deanery care home in Essex.
It has taken months of discussion and consultation for this guidance to be produced - the idea was raised in 2013 and agreed last year.
The 11-page guidance, which also covers non-covert recordings, says:
If people do have concerns, they should be raised with the provider of services first and regulators such as the CQC
Equipment should only be used in a person's private room
Permission should be gained from the individual being cared for first - if they are unable to give consent, filming must be shown to be in their best interests
The privacy of anyone recorded needs to be considered, including staff and visitors
Andrea Sutcliffe, chief inspector of social care, said: "We all want people using health and social care services to receive safe, effective, high quality and compassionate care.
"Sadly, we know that does not always happen, and the anxiety and distress this causes people, either for themselves or a loved one, is simply awful.
"For some, cameras or other forms of surveillance, whether openly used by services or hidden by families, are the answer. Others feel this is an invasion of people's privacy and dignity. Many don't know what to do if they are concerned.
"I hope that this information helps the public to make the right decisions for them."
Care Minister Norman Lamb said: "Cameras have helped to expose terrible cruelty and neglectful care, and I welcome this new advice.
"Decisions about using surveillance are extremely difficult - there is always a balance to be struck between protecting people and respecting their right to privacy - but this information will help families to the make the right choice for them."
But Nadra Ahmed, of the National Care Association, which represents providers, said it was "disappointing" that the guidance had been produced.
She said care homes were not against filming being used in an open way.
But she added: "Covert surveillance is very difficult to swallow. We are going to encourage relatives and friends to do something secretly. That says there is no trust. Relationships in that service will mean nothing."