('Alarm systems? What are those? I don't detect any wards or magical traps, therefore I can just walk in and make a horcrux.')

Depending on the magical system he could well bypass them accidentally. In the Buffyverse, for example, runes designed to protect against magical detection also work against any form of modern surveillance. In the HP universe I would expect Harry's cloak to protect against any visual detection technology and a Voldemort strength anti-detection spell would probably also be sufficient. Pressure sensitive plates would be a different matter but may also be the sort of thing that a wizard would expect. In fact, a competent wizardly burglar would quite possibly levitate as a matter of course while on a job.