Anti-personnel mines were installed along approximately half of the border's length starting in 1966; by the 1980s, some 1.3 million mines of various Soviet-made types had been laid.[67] In addition, from 1970 the outer fence was booby-trapped with around 60,000 SM-70 (Splittermine-70) directional anti-personnel mines. They were activated by tripwires connected to the firing mechanism.