How does contagt avoid interference from wifi?

Due to the relatively high transmission power of the beacons and the short distances, there is hardly any interference. contagt has also tested the system in trade fair environments with hundreds of WiFis.

Also the other way around, the BLE grid does not disrupt the WiFi infrastructure. The very short beacon frames at very long intervals (approx. 250-300 ms, depending on the configuration) are negligible for the activity of a WiFi network. 5GHz WiFi networks do not collide at all.