I have seen the glass here that goes opaque with the touch of a switch. The village I live in has this glass in rear of our ambulances. It is now a fairly standard feature on modern ambulances, as sometimes you want privacy for the patient.

There are also companies that sell a similar produce for interior and exterior household windows. These are quite costly though.

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2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp