This depends on the settings on your wireless devices. A Sitecom range extender transmits a separate Wi-Fi signal, with its own network name and network password. On many wireless devices (such as laptops and smartphones) you can select which Wi-Fi network should be connected to automatically. The network you select will be chosen whenever possible. 

Some users assign their router and range extender the same network name and network password. They also set their wireless devices to always connect to this ‘network’. In this situation many wireless devices try to connect to the network (your router or your range extender) they detect has the most powerful signal. This often depends on where your wireless device is located with respect to the devices (router, range extender) that all have the same network name. When configured this way, your wireless device will often automatically switch between wireless device connections to achieve optimum reception. This switching between Wi-Fi signals can sometimes be perceived as a nuisance because the connection may be lost during the switch.