Voters enter a booth and pop a clear glass marble into one of three drums representing the candidates, instead of a putting a ballot paper into a box.

As the marble falls into the drum, it hits a bell so officials can tell if anyone votes more than once.

"It's a unique system introduced in 1965 because of Gambia's high illiteracy," Gambia's chief electoral officer Kawsu Ceesay told the BBC.

The bell resembles a bicycle bell so bicycles are banned from around polling stations to avoid any confusion.

"Three drums representing the three presidential candidates will be in the compartment attached to one another so they can't be lifted to see which is heavier," he says.

"The drums are painted in the colour of the candidate's party and have their photograph and party symbol."

Incumbent President Yahya Jammeh's drum is green and his rivals Ousainou Darboe and Halifa Sallah are yellow and grey respectively.

Sand or sawdust is also put into the bottom of the drum before it is inspected by party agents and shut with numbered seals so that a second sound is not heard.