As an alternative to HTTP/HTTPS requests, you can "ping" checks by sending email messages to special email addresses.
By default, Healthchecks.io will consider any email received at the displayed address as a "success" signal. You can also configure Healthchecks.io to look for specific keywords in message's subject line to decide if the message is "success" or a "failure" signal. You can set up the keywords in the Filtering Rules dialog:
Consider a cron job that runs weekly and sends weekly newsletters to a list of email addresses. You have already set up a check to get alerted when your cron job fails to run. But what you ultimately want to check is if your emails are getting sent and delivered.
The solution: set up another check, and add its email address to your list of recipient email addresses. Set its Period to 1 week. As long as your weekly email script runs correctly, and there are no email delivery issues, Healthchecks.io will regularly receive an email, and the check will stay up.