Can 4 wire i3 smokes be used on the Silent Knight SK-4?
Yes. Acording to this https://usalarmdetection.com/products/silentknight/conventional/Silent%20Knight%20SK-4%20data%20sheet.pdf data sheet you can use two and four wire i3’s
In general, 4 wire detectors are compatible with basically anything. The alarm and power are separate so the alarm contacts are like pull station contacts