There are probably Android devices which make use of ARM's TrustZone [1]. Apple's Secure Enclave is a bit more thorough, though, because it actually uses a physically separate co-processor running a custom L4-based microkernel with a secure boot process. It is hardware isolated from the rest of the system, and uses a secure mailbox and hardware interrupts to communicate. Whereas ARM TrustZone appears to be implementable entirely on a single CPU.
