In today’s busy electronic world, there are numerous sources of stray microwave signals. Some of these sources are security systems, cell phone towers, and automatic door openers at supermarkets.
Most door openers at supermarkets operate right in the radar band, so they are actually a good way of testing your detector. You will typically get a warning when driving by.
Most false alerts will occur in the city, and you can turn on City Mode to help reduce false alerts.