A braille watch is a portable timepiece used by the visually impaired

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

 to tell time. It is used by touching the dial and noticing the embossments. Both analog and digital versions are available. The analog type differs from the ones used by the sighted in that it lacks the protective glass cover and the clock-hands are constructed to not be susceptible to movement at the mere touch of the finger that a blind person uses to observe their positions.
In the other form, the dots (like braille script

Braille

The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...

) keep changing position as time changes. In this case, one must understand the Braille alphabet to make use of such watches.
Nowadays, electronic talking watches, which literally tell the time at the touch of a button, are more popular among blind people.