Wired Magazine has an interesting story about a Soviet-era doomsday device that is apparently still active.  As reported there, the system

was to guarantee an automatic Soviet response to an American nuclear strike.

The system, called Perimeter (and also known as Dead Hand in Russian), is not widely publicized, due in part to the Russian penchant for secrecy.  It consists of nuclear missiles in hardened silos, ready to deploy if certain criteria are met (a breakdown in communications, earthquake-type shocks from nuclear detonations, and the like; with a human hand making the final decision to activate).

Why was it developed?  One reason cited in the article was for internal reasons:  the device would help stop Soviet hot-heads from launching a strike before it was proven that an attack had occurred.  Is it a danger now?  Probably.