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There are only three bursts of about 1 second length here. This shows that the activity in the band varies a lot and in my mind strengthens the case for believing that the main contribution is from car keys. But of course, one cannot be certain without decoding the bursts. That is possible for weather stations, as shown by Gough Lui in the article "RTL-SDR: 433.92Mhz ASK/OOK Decoding of Various Devices with rtl_433". The bursts can easily be heard if the receiver is set for Wide FM, as shown in the settings of SDR# in the image above.
Thanks to all viewers who have made the former blog post the most popular on my blog for this week. Thanks also to the RTL-SDR blog which gave it publicity in the blog post "Looking at the 432 to 438 MHz ISM band".