PIR Sensor ultra sensitive

While electronics would be cool, if you can't localize the point of entry based on sightings, I would go with a simpler approach.  They could also be "replicating" inside. 

You might be able to secure the perimeter of your house with a high fragrance spray.  If they track by pheromones, this will disrupt the trail.  The Dollar Store has a lavender cleaning spray that even I consider a bit over the top.  With the consistency that you have, you could even do zones to further narrow the points of entry.     A long time ago, I lived in sub-standard military housing and we had cockroaches.  One of the ways that we kept them in check was to go visit family.  Clean before you leave.  ZERO food for a few days.  Spray the perimeter immediately upon return - even before unloading the car.  The defensive perimeter worked.
When we lived in Texas... nothing worked - because they came in through the crawlspace under the house.  Boric acid (powder) and running shoes.  Yup.  I got pretty accurate throwing a sneaker at the cockroaches - a trick I learned living in a rental mobile home in North Carolina.

My final encouragement is the stick vacuum - with crevice tool.  Any place you find the bugs, vacuum every crevice anywhere near.  Spray with that overpowering lavender spray.  As the shampoo bottle says... lather, rinse, repeat.  Being bald, that's funny to me.  Good luck. 

According to Google they don't breed inside and they don't eat inside, they are just looking for dry place to spend the winter I think. (What can we believe anymore these days!) I think I agree from what I have observed about them.

Tried all sorts of essential oils (but not lavender) to no avail. I would bet one of the neighbors has tried it tho.....

Those were funny stories about the roaches.

There were 3 inch, huge ones, on these merchant ships I worked on in hot climates. Luckily they stayed in humid fan rooms!

tonyd512 Bummer. One strong scent should be as good as another. Dawn dishwashing liquid has been a magic elixir for many other things.. maybe that.  Again, I wish you success.

A friend of mine suggested this radar detector:

LD2410 sensor

Couldn't find anyone using it for bug detection online with a cursory search....

Thoughts anyone?

Another possibility might be Orange Oil.  It has been used to control (or discourage) termites.  We have been using in garden to control Fire Ants.

That's the sensor that was mentioned earlier as an example to read up on:

/technologies/embedded/b/blog/posts/experimenting-with-microwave-based-sensors-for-presence-detection#mcetoc_1h0c077bia

The LD2410 certainly can detect mouse-sized objects, but I didn't try anything smaller at the time. You'd need to give it a shot (or some other microwave sensor, if there is any that looks more suitable out there) to see if it is suitable, since probably the manufacture doesn't even have data for that (a lot of these low-cost microwave sensors might have been designed for human presence). There's a chance it could work, but really needs experimentation. A camera based sensor is possibly more effective, but needs processing as discussed by a few people.

Sorry this is a lot of information to digest

Thank you so much for the help

No problem, some of the info on engineering websites will be hard to follow initially, plus it's just the nature of the beast, that many raw sensors require some testing or bits of additional hardware/processing/software, many are not pre-packaged and configured, but if you have any questions people here can help. 

I've used some radar sensors from DFRobot. They have a unit https://www.dfrobot.com/product-2648.html similar to your image. I haven't used this device but I was curious of limit .75 meter minimum. How successful was your sensor on small object being close to the sensor.

I've used some radar sensors from DFRobot. They have a unit https://www.dfrobot.com/product-2648.html similar to your image. I haven't used this device but I was curious of limit .75 meter minimum. How successful was your sensor on small object being close to the sensor.

Hi Sean,

That's the one! I got mine from AliExpress, where it's known as HLK-LD2410, it looks identical.

I suspect there would be no issue with detecting objects nearer than 0.75 meters but with an inaccurate distance measurement perhaps, but to be honest I can't recall much. I didn't do a lot of testing at the time, I was more focused on getting the code operational to make it work with Arduino, Pi Pico and PC, so that I'd have some flexibility to experiment later, and then I moved on to something else. I'll have to revisit it, and give it a shot (possibly at the weekend).

It's for sure a fascinating sensor, well worth experimenting with.