Alarm Timers for the earliest electric alarm systems are
often confused with time locks used in safes and vaults. However,
alarm timers such as this 1890 model from the New Heaven Clock
Co. are easily identifiable by their lighter insulated construction,
single movement, and set of electric contacts.
The electrical contact on this early design is visibility
extending from the top of the case. When the 24 hours timer
runs down, this electrical contact will move from the left
to the right (as shown), at last, the alarm timer disconnects
the electric power of the alarm system.