The Ofcom Wi-Fi checker tests the quality of your wi-fi and also provides guidance on how to improve signals.
Research it released today shows over five million UK homes could improve their signal.
In a statement, it said that broadband can be slowed by fairy lights, microwave ovens, baby monitors and even a lamp.
The app is available for both iOS and Android, via the Apple app store and Google Play.
In separate news, Ofcom said that rural areas are still badly off for broadband speed. But BT is testing speeds in Swansea using G.fast, that can motor along at as much as 500Mbps.