This is an aftermarket gas meter pulse transmitter (reed contact) compatible with meters: Apator Metrix. (see on the picture) for G1.6, G2.5, G4, G6, G10, G16, G25, G40 sizes.
This pulse transmitter can be installed by non-trained personnel without breaking the seal and does not contain a magnet.
It is easy to integrate into various readout systems, like ESPhome and HomeAssistant. It provides a switch output after a predefined gas amount went through the meter. The pulse to gas volume conversion is noted on the specific meter.
The pulse module can be fixed without opening the transmitter nest.