The invention relates to a method for monitoring a safety circuit and a monitoring device for a safety circuit of a lift system. The invention is based on a monitoring device (17) for a supply voltage of a series connection (2) of switches (3) for monitoring the safety of devices (18) serving the lift operation. Safety relays (4) are connected to the end of the series connection (2), which generate signals for controlling (7) a lift according to the switching state of the switch (3). The supply voltage is set in such a way that the voltage is constant across the safety relays (4). Since there is an upper limit to the supply voltage that can be made available from the voltage source (10), the supply voltage is monitored and an error notification is generated when an upper limit value is reached. According to the invention, in order to permit high levels of availability of the lift system, at least one further parameter of a curve of the supply voltage is determined and evaluated.
