Roll Down security Shutters price
https://www.storeboard.com/blogs/general/how-the-10-worst-protection-roller-shutters-fails-of-all-time-could-have-been-prevented/979475
Or the louvered slats of hacienda shutters can be fairly intelligently readjusted so that also during the day, when you need light to be allow into the area, an observer's view is disturbed, blocking their view