One of the best Security Systems you can buy on Amazon is certainly the Arlo pro http://amzn.to/2vFnVsn from Netgear.
It is Amazon best seller and top rated. Here is a review https://www.pcmag.com/review/351867/netgear-arlo-pro
Also good are
- the cameras from Vimtag http://amzn.to/2gl1zKG
- the Nest Cam Indoor http://amzn.to/2wFAOY4
- the cameras from Amcrest http://amzn.to/2wOu8ar
For a wider choice of smart home security products you can check this article on safety.com
Not many systems have a monitor included, but many solutions have the possibility to connect any smartphone or tablet, so basically you can use your own tablet as a monitor, or purchase a cheap one to do the job.
The Arlo pro even allows to connect with Alexa and work with voice commands.
Security metal detectors are basically used to detect any metal object in the security zones. The most common security metal detectors are using very low frequency or VLF technology.