[Deprecated] BI Control - Local Blue Iris control

An Alexa Routine with a Custom Action might do it for you. Use something like the Virtual Switch with Motion:

That would then allow you to trigger an Alexa Routine and you could use a Custom Action to silently speak to your Echo:
https://www.amazon.com/gp/help/customer/display.html?nodeId=GLXY7RFX3L5GH2VR