Work on fixed installations (faste installationer) has to be done by an autoriseret elinstallatørvirksomhed (authorised electrical firm). Ask whether they hold the authorisation themselves or bring someone who does, and get that on the invoice.
Køge is the hub along Køge Bugt, with jobs in town and nearby places such as Karise. Many houses are detached. A drive along the coast is common. The same 4 businesses as the Danish page: Boje Elteknik ApS, EL-JENSEN A/S, Midt & Nordsjællands El-Service ApS, SEMPA EL-INSTALLATION ApS.