What is a curfew from medieval towns?

In places like Venice, Italy it was a bell rung from a bell tower to tell the Jewish residents that it was time to go home. They had a Jewish section of Venice and that's where the people lived. At one point there was also a fence with a gate and they were locked into their section at night. The only way people could know a certain time was with the ringing of a bell. The wrist watch hadn't been invented nor was the use of clocks, so bells were rung. Even today most places in Europe still ring out the time and you count the number of rings. It is very handy.