Not the very cheapest for this (lowest $50.99) but still a decent price.
20% off coupon (no code required) auto applied at checkout.
Is under Home Improvement category so Cashrewards / Shopback applies I believe.
Note this is the Google Assistant, Alexa version not the Homekit one.
Mod: Warning - Be aware of safety standards and laws regarding the use and installation of this before purchasing.
Have you figured out how to get an alert if the door is left open for too long?
I have the unit from aliexpress and running Tuya app.