Inode notify (inotify) is a Linux kenel subsystem which provides APIs to to monitor filesystem events. Besides communicating with such APIs from proper programming languages, it is possible to take advantage of the exposed functionalities by using some explicitly designed command line tools such as inotifywait, which can be easily installed in all the major Linux distributions.
ACPI is the acronym for Advanced Configuration and Power Interface; as a standard, it was first implemented in the year 1996, as a successor to APM (Advanced Power Management). As a main feature, it brought the ability to handle power management at the operating system level, whereas before it was handled in BIOS. Some ACPI events on Linux are, by default, handled via systemd-logind, but more complex configurations can be achieved by installing and running the acpid service.