A safety device for regulating the supply of electricity and/or fuel to an appliance. Electricity and/or fuel may be supplied to an appliance for a period of time responsive to a user operating a user operable control means, such as a button. The safety device will cut off the supply of electricity and/or fuel after a first period of time unless the user operable control means is operated again to extend the period of time for which the regulator means allows the supply of electricity and/or fuel. Thus, the user must periodically operate the user operable control means if the appliance is to continue functioning. The safety device may function differently at different times of the day. The safety device is particularly useful with electric or fuel burning cookers, to reduce the risk of fire when the cooker is inadvertently left unattended.