Updated version makes sure the response code is 200. Also saves any possible false alarms to a file so we can evaluate how to fix those.

gistfile1.sh

#!/bin/bash

api_key="your Prowl API key goes here"

cd ~

testSiteForChanges () {

    ls "old_page.html" 1>/dev/null 2>/dev/null
    if [ $? -eq "1" ] ; then
        curl $1 --silent -o old_page.html
    fi

    response=$(curl $1 --write-out %{http_code} --silent -o new_page.html)
    diff old_page.html new_page.html 1>/dev/null

    if [ $? -eq "0" ] ; then
        page_changed=0
    else
        if [ $response -eq "200" ] ; then
            page_changed=1
            cp new_page.html false_alarm.html
        else
            page_changed=0
        fi
    fi
    rm new_page.html
    
    return $page_changed
}

# testSiteForChanges "http://www.cnn.com"
testSiteForChanges "https://developer.apple.com/wwdc/"

    if [ $? -eq  "1" ] ; then

        url="https://api.prowlapp.com/publicapi/add?apikey=${api_key}"
        url="${url}&application=WWDC%202012"
        url="${url}&event=Registration%20Open"
        url="${url}&description=It%20is%20time...%20maybe."
        url="${url}&priority=2"

        curl -k -s ${url}
    fi