StatHat can send alerts directly to one of your Slack channels.
Note: StatHat will be an official integration soon, but until then you need to use Slack's DIY Integrations.
On Slack, go to Configure Integrations. Scroll to the bottom to the DIY Integrations section and add an Incoming Webhook. Choose a channel and you'll get a webhook URL. Paste that URL into the StatHat Alert Destinations form for Slack.
Now you're all set to configure how alerts get sent to Slack. You set the defaults on the Settings page.