For a firearm sighting device with an electrical illumination device that can be turned on and off by means of a switch, the switch is embodied and arranged in or on the sighting device such that, for the conventional attachment of the sighting device on the firearm, the switch is activated mechanically to turn on the illumination device by the activation of an actuator provided in or on the firearm for setting the firearm into the armed state. By disabling the firearm, the switch is activated mechanically to turn off the illumination device. Preferably, the activation of the switch is performed using a non-contact method, for which, in particular, the configuration of the switch as a reed contact is suitable. The switch can also be part of a retrofit kit, by means of which a sighting device for a firearm can be equipped at a later time with the previously mentioned function. Here, the switch of the retrofit kit replaces a standard switch operated by hand separately from the firearm.