Chatter 2.0 reaches about 2 km (1.2 miles) with clear line of sight, and a few hundred metres in built-up areas. It uses LoRa (Long Range) radio communication, which trades data rate for range.
Open area (clear line of sight): up to about 2 km (1.2 miles).
Built-up areas (buildings, walls): typically a few hundred metres.
Indoors (same building): usually fine across a normal house or school.
Range depends on obstacles, interference from other radio devices, antenna orientation and the weather. For best results, keep the devices upright and away from large metal objects.