Today, I read on the rcgroups.com forum about some complains regarding the auto cut-off issues on the X5C quadcopter.
I decided to test this problem by myself because it can produce some unhappy things like the flyaway.
Syma X5C Auto Cut-off video
After few tests, the results were promising, every time I stopped the remote controller (resulting remote signal loss), in 2-3 seconds all the motors on Syma X5C got stopped by the protection circuit. That means no flyaway effect when the quadcopter is out of the remote controller range. Good work Syma!