The backstory (the whole reason this exists)

I live directly across from an elementary school, community center, and library on the backside on a street with no stop signs and no speed calming, and people absolutely rip through it. It's almost set up like a race track. So, I requested a speed study from the county back in 2022 (outside of city limits). They did one and the 85th-percentile speed of 25 mph, averaged 20mph so they basically said speeds were within limits and nothing would be done. This same study has been the answer every time I've asked for a stop sign or a speed bump since. I got two little kids who love to play outside and it's just crazy how people will drive 40mph+ like it's nothing.

In my opinion though, there were two major problems with that study:

1. It used one of those portable counters with the big black tube/box sitting in the lane. Drivers would it and slow down as they approach it so it functioned like a temporary speed bump. So it actually measured the one behavior you don't get the other 364 days a year. If they just would have left it, it probably would have solved my problem.
2. It ran for maybe 24 hours and in the summer while school was out. Way too short to capture normal traffic and none of the school traffic obviously

So I "built" my own radar detector that is permanent, basically invisible, runs 24/7 locally, and I own the data.

Hardware

• OmniPreSense OPS9243-A-PE — 24 GHz Doppler radar, the Ethernet/PoE variant
• Connected and powered off a UniFi USW-Flex 2.5G (PoE) that lives in my garage
• Weatherproof run: USBFireWire RR-125320 double-ended outdoor cable, with an RR-125310 adapter to break back out to the Flex in the garage.
• HA itself runs as a VM on Proxmox, with a local Mosquitto broker

Mounting

Had to buy this mount off Amazon and design and print a plate for it since it uses standard 1/4" connections. Plate just screws into the back of the radar detector then goes into the plate I printed.

The data pipeline

The OPS9243 publishes JSON over MQTT to a single topic (<serial>/json). Quick shoutout to OmniPresence for providing all the needed documentation on how to get this to point locally and not to their cloud. Anyway, two message shapes land on that same topic:

• Per-detection messages with DetectedObjectVelocity and direction
• Periodic TimedSpeedCounts summaries

On the HA side I've got template sensors for current speed and direction, plus a running speed log that keeps the last 50 detections as a list of dicts and renders them on a markdown card just so I can just keep that up and watch as I work during the day lol.

Aiming matters — and mine cheats in my favor

Doppler radar only measures the velocity component along its boresight, so a steep mounting angle introduces cosine error and reads low. I aimed mine nearly parallel to the road to keep that error tiny, and verified it by driving past at a known speed in my own car. It tracks scary accurate. Usually reports about 1mph under my actual speed.

Here's the part I love for my situation: any small error that does remain is always in the under-reading direction. It never reads high. So nobody at the county can accuse me of inflating the numbers. If anything, the real speeds are worse than what I'm logging.

Why local-first

No cloud dependency means it keeps running when the internet doesn't, nothing phones home, and the data is mine to do with as I please. Same reason the rest of my setup (UniFi + ESPHome + HA on Proxmox) avoids the cloud wherever it can.

What's next

More automations? I have one that alerts me when a speeder is going 35mph so I can grab the clip from the G6 180 and back it up to my NAS and add the speed they were going. Probably can automate the rest of that out.

Hue lights out front doing a red/blue light cop effect when a certain threshold is met?

Also, building proper speed histograms and time-of-day breakdowns so I've got a real dataset, not a cherry-picked 24-hour snapshot, to take back to the county. Long enough collection window that it can't be waved off as a fluke.

Honestly though, my new favorite thing is sitting on the driveway with neighbors at night, having a drink and yelling at speeders in real time. lol.

https://preview.redd.it/jo4icam0qi5h1.jpg?width=3024&format=pjpg&auto=webp&s=aad72385386c85e554348d213f3ff4e9a19d4159