There are three basic types of earpiece surveillance kits - the 1 wire, 2 wire and 3 wire.

1 Wire Surveillance Kit
A 1 wire surveillance kit has a single combined microphone & push to talk button that clips to your collar (2). From this button extends a wire with clip (3) that has the earpiece (4).

2 Wire Surveillance Kit
A 2 wire surveillance kit has a wire with a combined microphone & push to talk button (3) that can be clipped to your collar or can be run down your sleeve and clipped to your cuff.
There is a second wire that has the clip (4) with earpiece (5) on it. Some kits also have a second PTT button (2) that clips to your belt or pocket near the radio (1).

3 Wire Surveillance Kit
A 3 wire surveillance kit has one wire for the earpiece (3) with clip (2), a second wire for a microphone (4) that clips to your collar and a third wire for a PTT button (5) that runs down your sleeve.

Since the 3 wire kit has separate parts for each piece of the kit it offers the highest sound quality and durability. However, for typical work such as office use, light security, restaurants, floor managers, etc. a 1 wire or 2 wire kit will do the job perfectly.