This Pet Hacks Contest entry from [Andrea] opens the door to a great collaboration of sensors to solve a problem. The Cat At The Door project’s name is a bit of a giveaway to its purpose, but this project has something for everyone, from radar to e-ink, LoRa to 3D printing. He wanted a sensor to watch the door his cats frequent and when one of his cats were detected have an alert sent to where he is in the house
There are several ways you can detect a cat, in this project [Andrea] went with mmWave radar, and this is ideal for sensing a cat as it allows the sensor to sit protected inside, it works day or night, and it doesn’t stop working should the cat stand still. In his project log he has a chapter going into what he did to dial in the settings on the LD2410C radar board.
How do you know if you’re detecting your cat, some other cat, a large squirrel, or a small child? It helps if you first give your cats a MAC address, in the form of a BLE tag. Once the radar detects presence of a suspected cat, the ESP32-S3 starts looking over Bluetooth, and if a known tag is found it will identify which cat or cats are outside waiting.
Once the known cat has been identified, it’s time to notify [Andrea] that his cat is waiting for his door opening abilities. To do this he selected an ESP32 board that includes a SX1262 LoRa module for communicating with the portable notification device. This battery powered device has a low power e-paper display showing you which cat, as well as an audio buzzer to help alert you.
To read more details about this project head over to the GitHub page to check out all the details. Including a very impressive 80 page step-by-step guide showing you step by step how to make your own. Also, be sure to check out the other entries into the 2025 Pet Hacks Contest.
That’s one well-trained cat butler! :-)
Is it safe for the cats to be subjected to radar? I’ve heard to too many cat scans can cause cancer!
It’s far safer to scan the cats than try to use the cats to scan people. Even the chillest kitty will get cranky by the time they’ve been rubbed across even a small human.
The radar module chosen was developed for human detection. The radar power is about 13 dB, which means that at a distance of 10 cm the power density is about 0.16 mW/cm² (already below the public exposure limit) and at a distance of 50 cm about 0.006 mW/cm² (negligible). A 5G mobile phone is 5 to 10 times more powerful and works at a much closer distance. All sources consulted indicate no evidence of health problems.
my cat beats on the door like a bill collector.
Yeah! Mine sits at the door and beats his head against it until I open up. I feel your pain.
Still doesn’t beat just not letting your cats outside.
My last two little guys were abandoned as kittens and, consequently, they were petrified of the outdoors. However, most cats love being outside. I see no problem with that.
There are two issues that I can think of immediately:
puts them at risk of getting hit by vehicles or otherwise hurt
IIRC there are reports that the combination of them having shelter and free food but still hunting for fun has led them to be devastating for many species
Anon:
When you get to hell, your jailed cats will be there.
They will be the size of Tigers and you will not be able to escape by dying.
Your tasty tasty liver will regrow, quite painfully.
They sit in the window dreaming of freedom all day.
But they know if they are denied, their dark lord will help them get you.
Better be right in the ‘guess the correct religion’ game.
I bought a battery run wireless doorbell for 5 € and fitted the button between two small cutting boards, separated by a rubber foam band. The contraption is of the size of a sitting cat. The foam is just as dense as necessary to give way with the weight of our cat and have the button sqeezed. Ding-dong, the cat is here!
Some of our friends use it now, too.
In my view it’s a funny thing but not necessarily for me, our cat 🐈 notifies us itself if it wants to go inside “MEOW”
Wow ! what a well trained and educated little cat! Mine are more like wild cats barkling (yeah I know, go figure!) and desperate scratching my door or jumping to get the window like no tomorrow, just to show me off they got a prey. It can be a chicken, a bird, a lizzard, usually they run away as hell when I tell them I want the half of it.
I built something similar for my mother. I was limited to battery power so I used PIR instead of radar. PIR turns on the microcontroller, which then scans for BLE tags. If it gets a match it triggers the “doorbell”, which is a light up house-shaped bit of acrylic. Lights up a little cat shape so you know which door the cats are at.
Battery status is sent so it’ll blink red if low on power. Also blinks red if it hasn’t heard from the sensor for a while. Battery is LiPo and USB charged.
Works well. I added phones so it works as a human detector as well.