Impeneterable security systems are normally made up of visible beams across a room making it difficult, but not impossible for the hero to walk through. No-one ever has motion sensors which would go off straight away.
How about, visually, every police car parked at an incident has to have its red and blue lights flashing. Even if the incident has finished and the hero and heroine are talking at the end. Visually eye catching. Not something that happens.