I've always been confused with that too. That Pelican thread is helpful, but not 100% accurate. Some of those DMEs are actually Siemens units, not Bosch.
I've never seen an EWS1 car. EWS2 is the easy-to-defeat one <96 IIRC. EWS3 is part of Bosch's OBD2 DMEs >96.
The key switch ring antenna is a clipped-on ring around the ignition switch (under the steering column covers) that reads the (RFID?) chip in the key. The key sends a code via the ring antenna to the EWS unit, which then enables the DME. The keys are the same externally, from what I understand.