There are certainly people that sell useless tools that purport to be able to detect cameras.
There are certainly devices that can detect localised electric fields, wireless transmissions or make it relatively easy to spot shiny surfaces (such as camera lenses).
…but, and I say this with absolute confidence; there is no device that exists that can detect if you are being observed or not.
So, to some degree, it may be possible to find common wireless cameras, and if you’re some DIY house owner installing their SPY PRO secret camera from Amazon for $50, you can probably find it.
…but, the point the parent comment is making is that there are, and, increasingly will be, cameras you won’t be able to detect.
You’re best off to operate under the assumption you are being filmed when you hire a house, and, increasingly, just when you go around your daily life.