I recently learned the following interesting thing about the Transitautobahn (the motorway connecting West-Berlin with West-Germany). To enter or leave the GDR, you had to pass the Marienborn controll point [0][1]. This facility was outfitted with underground tunnels and an extensive conveyor belt system to transport passports from the gates to internal checking facilities. More interestingly, the Stasi had very large gamma-ray scanners [2] ("Gammakanonen") installed on the lanes [3][4] which were used to check passing cars for hidden persons. These scanners were quickly removed after the border was opened in 1989.

[0] https://upload.wikimedia.org/wikipedia/commons/5/51/Grenz%C3...

[1] https://en.wikipedia.org/wiki/Helmstedt%E2%80%93Marienborn_b...

[2] https://en.wikipedia.org/wiki/Cargo_scanning

[3] https://img.braunschweiger-zeitung.de/img/helmstedt/crop1502...

[4] https://www.mdm-online.de/tempcache/t_fc_lg_sets_bilder_2404...