This study compares the Lucerne German allophones of Middle High German <l> using data from the crowdsourcing smartphone app Dialäkt Äpp, to those of the Linguistic Atlas of German-Speaking Switzerland. In doing so we examine language change in real-time across c. 70 years. In the north of the Canton of Lucerne, use of /l/-vocalisation has receded, whereas in the west, and in and around the city of Lucerne, /l/-vocalisation occurs more frequently than at the time of the historic atlas. Both age and sex differences were found to be statistically nonsignificant, though older speakers tended to vocalise more. Generally, however, we report substantial areal heterogeneity which we suspect is due to the Canton’s geographical location in a dialectal transition zone, increased personal mobility, and the growing presence of broadcast media in dialect.