Not the OP, but when we built this functionality for Heii On-Call https://heiioncall.com/outbound_prober https://heiioncall.com/outbound_prober we made sure (1)

Not the OP, but when we built this functionality for Heii On-Call https://heiioncall.com/outbound_prober https://heiioncall.com/outbound_prober we made sure (1) the User-Agent string points you to this page, (2) the User-Agent contains a unique string which we can decode and track back to the unwanted HTTP probe configuration on our end, and (3) also obeys /robots.txt. Trying to be a friendly robot :)