There are many sites which already does this. During that situation when I missed a slot, I didn't want to take any chances again by using sites like visualping. I trusted my script and twilio API to work.

First I thought to ring a loud alarm connected with a Pi, but then it will be limited to my apartment. So I went with twilio to give me a phone call. Because I should act immediately and time was of the essence. Emails or SMS might go unnoticed.