Howdy,A solution to this problem is in the debdiff attached, it is easily backported as it leaves support for the old location of laptop-detect, but otherwise will use the new location. This is also what has been uploaded to Ubuntu.
~Unit 193 Unit193 @ OFTC Unit193 @ freenode
diff -Nru numlockx-1.2/debian/55numlockx numlockx-1.2/debian/55numlockx --- numlockx-1.2/debian/55numlockx 2014-08-11 06:08:41.000000000 -0400 +++ numlockx-1.2/debian/55numlockx 2018-05-20 11:44:06.000000000 -0400 @@ -20,7 +20,11 @@ ;; *) NUMLOCK=on - ltd=/usr/sbin/laptop-detect + if [ -x /usr/sbin/laptop-detect ];then + ltd=/usr/sbin/laptop-detect + else + ltd=/usr/bin/laptop-detect + fi [ ! -x $ltd ] || ! $ltd || NUMLOCK=off # Enable numlock for USB keyboard on laptop if [ -f /bin/udevadm ] ; then diff -Nru numlockx-1.2/debian/changelog numlockx-1.2/debian/changelog --- numlockx-1.2/debian/changelog 2014-08-11 06:08:41.000000000 -0400 +++ numlockx-1.2/debian/changelog 2018-05-20 11:47:27.000000000 -0400 @@ -1,3 +1,11 @@ +numlockx (1.2-7.1) UNRELEASED; urgency=medium + + * Non-maintainer upload. + * d/55numlockx: Adjust to find laptop-detect after move to /usr/bin + (Closes: #894481) + + -- Unit 193 <unit...@ubuntu.com> Sun, 20 May 2018 13:44:27 -0400 + numlockx (1.2-7) unstable; urgency=medium * Rewrite USB keyboard detection using pure udev (Closes: #757475).