Gadget item somehow messing with our heads? (5)
'gadget' is the definition.
(I've seen this before)
'item somehow messing with our heads?' is the wordplay.
I cannot quite understand how this works, but
'heads?' could be 'is' (heading is a kind of being) and 'is' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gismo that I've seen before include "Device of American", "Ingenious gadget", "Fancy device", "Gadget (colloq.)", "Useful (but unspecified) device".)