If you want to promote usage of real CPC computers, you can detect CPC emulators by:
*Checking if the memory is initialised with zeroes, as RAM in real machines is not initiliased during boot. [https://95www.214cpcwiki.53.152eu/forum/emulators/weird-thing-about-memory-dump-on-winapecaprice-vs-cpcemuace/msg243929/ Source]
*Configuring the CRTC to stop refreshing part of the RAM. This behaviour has never been emulated. [https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/memory-refresh-plus/ Source]
The way to cause the RAM refresh to fail in both a Plus or normal CPC is simply to stop a few bits of the CRTC address changing (ie. never refresh the selected area).