Oh, one more thing: you can send email to _any_ address, not just your personal one.
The only Notification Channel that you can create directly in an Alerting Policy is email, BUT...
If you create a Notification Channel for Slack in Stackdriver Account Settings > Notifications > Slack (look at the top bar of the right hand panel, the shortcut is https://app.google.stackdriver.com/settings/accounts/notifications/slack)
then you ought to be able to configure any alert notifications to to that Notification Channel.
The same thing is true for Campfire, PagerDuty, SMS, WebHooks, etc. Once you create the channel, you can use it for alerting (and you can send alerts to multiple channels).
My apologies for being so late to comment on this, I just noticed the post... I hope that this helps!
This is definitely on our radar for Uptime! Would you need more than POST (I.e., PUT, PATCH, etc)? What kind of data would you envision sending in an Uptime check?