ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
From previous post:
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.
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.