CheckIfDockerChecksumWasUpdated.sh

#!/bin/bash

touch /tmp/Recent.xyz

while true
do
    echo "Checking again..."
    wget -q https://apt.dockerproject.org/repo/dists/ubuntu-xenial/main/binary-amd64/Release -O /tmp/Release.xyz
    if test /tmp/Release.xyz -nt Recent.xyz; then
        mplayer /usr/share/sounds/ubuntu/stereo/phone-incoming-call.ogg
    fi
    sleep 5;

done

There is weird issue with the directory at https://apt.dockerproject.org/repo/dists/ubuntu-xenial/main/binary-amd64/
If you notice, there is no file called "InRelease" shown over there.

However, if you

$ wget -S --no-cache https://apt.dockerproject.org/repo/dists/ubuntu-xenial/main/binary-amd64/InRelease
--2016-06-02 17:27:28-- https://apt.dockerproject.org/repo/dists/ubuntu-xenial/main/binary-amd64/InRelease
Resolving apt.dockerproject.org (apt.dockerproject.org)... 52.85.19.64
Connecting to apt.dockerproject.org (apt.dockerproject.org)|52.85.19.64|:443... connected.
HTTP request sent, awaiting response...
HTTP/1.1 200 OK
Content-Type: text/plain
Content-Length: 2576
Connection: keep-alive
Date: Thu, 02 Jun 2016 13:32:44 GMT
x-amz-meta-s3cmd-attrs: uid:0/gname:root/uname:root/gid:0/mode:33188/mtime:1464865616/atime:1464826124/md5:124af13d48d3b02cea1d01d4596e73fd/ctime:1464865616
Last-Modified: Thu, 02 Jun 2016 11:09:23 GMT
x-amz-version-id: kM1R5Po2.wkPK5Ic5hT.4J_QqlmIdA3g
ETag: "124af13d48d3b02cea1d01d4596e73fd"
Server: AmazonS3
Age: 211
X-Cache: Hit from cloudfront
Via: 1.1 e5d27f3fb83b3b7e4d92ffc70e7b5a1f.cloudfront.net (CloudFront)
X-Amz-Cf-Id: W5jsFWNhTMZlkuWUqg1cwSb-7x0gYmopmAog1gMDsiI9vJlM7Tt5FQ==
Length: 2576 (2,5K) [text/plain]
Saving to: ‘InRelease’

InRelease 100%[==========================>] 2,52K --.-KB/s in 0s

2016-06-02 17:27:28 (454 MB/s) - ‘InRelease’ saved [2576/2576]

That is, Cloudfront serves a cached file, the one that used to show up earlier with the wrong checksums.
In other words, although the file InRelease is gone, Cloudfront still serves it.