See [archlinux](https://wiki.archlinux.org/title/Power_management#Hooks_in_.2Fusr.2Flib.2Fsystemd.2Fsystem-sleep)

Put something in `/usr/lib/systemd/system-sleep`, for example
```bash
#!/bin/sh
case $1/$2 in
  pre/*)
    echo "Going to $2..."
    ;;
  post/*)
    echo "Waking up from $2..."
    ;;
esac
```