Modifying the Hytera SM18N4-EX
Ex series accessories are often available on sites like Ebay and command lower prices than their standard counterparts due to the incompatibility with the more popular non-Ex radios.
The Hytera Ex range of accessories have 3 additional pins that inform the radio of an Ex device being connected. You can see them in the diagram to the left, circled in red. Pin numbers 3, 4 and 13.
When connected to a non Ex radio body, an "Unknown Accessory" warning is shown and the acessory will not function.
Cut some small peices of insulation tape (I used blue for contrast here) and place them over the pin locations on the radio body.
Non Destructive Method
Use a small pair of pliers to remove the pins that are not needed. Your accessory may not have all of the Ex pins populated but remove the ones that are.
The Ex accessory now works with a standard radid body and has full functionality.