Are you looking to link this with a current system, or you creating a new system from scratch?
Is this for an indoor system or an outdoor system?
There are a number of solutions available for motion detectors compatible with Alexa on Amazon. I would recommend looking at the options available there, then reading the reviews and contacting the manufacturer with specific questions about your particular setup before you buy.
Please report back which system you decided to go with and how it’s working for you!