*Playing with the "floating" bus
*Focusing on the minute details in [[Z80]], [[CRTC]], [[8255|PPI]] and [[PAL16L8|PAL]] chips. They are most often wrong in emulators
*Examining the [[FDC]] chip. It is only replicated more or less superficially in all emulators because the internals of the chip are still unknown. Many emulators don't even support the FDC SCAN or FORMAT commands
Combining these methods will definitely get you a 100% success rate in detecting emulators, even the toughest ones.