Some of the Pretoria gates (the ones in the north built before the etag fiasco) are linked to etolls. i.e. That automatic boom opens when detecting an etoll tag.
Bakwena use also etags as what Havoc said, and if I drive under the GIFP gates it beep 3 times, to say the gantry and my tag talks, but isn't registered, so no money taken, also some gates like the one before the Hugenote Tunnel, beeps, but no money taken.