A smoke producing device for detecting leaks in a fluid system comprises a smoke producing chamber and a fluid reservoir for containing a smoke producing fluid. A heating element is provided within the smoke producing chamber. The chamber has a pressurized gas inlet for receiving a pressurized gas and an outlet port for conveying pressurized gas and/or smoke out of said chamber. A fluid transfer device has a first portion disposed within the fluid reservoir and a second portion which is adjacent and/or in contact with the heating element. The fluid transfer device is a capillary flow device which conveys smoke producing fluid from the fluid reservoir to the vicinity of the heating element primarily by capillary action.