Display Message If Certain Value Returned

I am looking to return a pop up box if a certain value from my select box is picked
PHP Code:
var inpObjs = document.getElementsByName('typeofbike[]');
validChars=/^[a-zA-Zd]{16}$/;
for(i=0; i < inpObjs.length; i++){
if (typeofbike== 'I will be using my own bike')
Alert ("If using your own scooter / bike for training, it must be of a road worthy condition, to our instructors satisfaction. Please also bring with you your current CBT certificate, a valid certificate of insurance, MOT (if applicable), and also ensure the vehicle is displaying a valid tax disc and two legally sized 'L' Plates");
return false;
}}