The PaintChecker measuring system has a multi-level safety design. A safety chain prevents the laser from being switched on by accident. Only when all the conditions, such as laser key on, emergency off released and release are active, can the laser be switched on. In addition, further door contacts can be integrated into this chain. In the light source activator there is, in addition, electronic pulse length and repeat rate limitation for the generation of laser pulses. This is to prevent the measuring device from being switched on via software in a non-permitted operation mode. A message output "Installation safe" indicates that the laser has been switched off properly. The laser power supply contact is monitored to check this. Therefore simple errors such as those in the EN954-1 class 3 will be recognised.