This shape and pattern are the characteristics of the late Yuan Dynasty and the early Ming Dynasty. Opening the door is an old thing, but it is not a protective mirror, it is the support of the knocker. All the buildings in Cuanxia Village, Zhaitang Town, Mentougou District, Beijing have retained the original features of the Ming Dynasty. I have been there twice, and almost every family has such a knocker. As I have never seen anything like you in the market, the price is not clear. Just now, I sent your photo to Mr. Wang Weidong, an antique connoisseur, and his market price was 3,000-4,000 yuan. For reference only!