520 Hz

This exquisitely generic smoke alarm displays on its face the required audio frequency for such devices: 520 Hz. If the typography included a symbol to show the frequency is a square wave, that would likely be too much of a design element, shifting the low-budget gadget’s appearance from infrastructure-rote to minimalist-austere. Perhaps the thing could simply read “smoke alarm,” and thus enter the realm of a Repo Man movie prop. If only the electrical outlets down at floor level read 60 Hz, but alas they are blank.