All I get after following the documentation, is a compiler error:

CMake Error at /data/external_components/fd3660ad/src/cpp/espectre_git_version.cmake:62 (message):  
  Unable to resolve ESPectre version from git describe, and the SDK header is  
  not stamped.  Fetch numeric tags (`git fetch --tags`), pass  
  -DESPECTRE_GIT_VERSION=..., or set ESPECTRE_GIT_VERSION in the environment.  
  fatal: No names found, cannot describe anything.  
Call Stack (most recent call first):  
  /data/external_components/fd3660ad/src/cpp/CMakeLists.txt:101 (include)  
  /data/external_components/fd3660ad/src/cpp/frontend/esphome/components/espectre/CMakeLists.txt:6 (include)  
-- Configuring incomplete, errors occurred!  
cmake failed with exit code 1, output of the command is in the /data/build/testesp/build/log/idf_py_stderr_output_12018 and /data/build/testesp/build/log/idf_py_stdout_output_12018  
ERROR Component discovery failed  

Edit: Managed to work around it. Now it actually detects movement! Just be aware this project looks like it's cooked up with a lot of AI assistance. There's a million pages of documentation, mostly convoluted and repetitive while telling slightly different things to do... And a compiler error is never a good first impression... It seems to work, though!

Now I have to find a few spare ESPs, which aren't already doing BLE or something, and see what kind of strain it puts on my wifi network.