Go to Apps > All Apps.

Search for Text Field Rules > Click on it > Click Install.

Accept the needed permissions.

Using the dropdown, choose the sign-in flow(s) for which you want to set up short answer rules:
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In the case above, we've only selected one sign-in flow, "Visitor."
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Select the sign-in field(s) for the flow(s) you selected in step 1 for which you'd like to set up short answer rules. Then, enter the logic you'd like to check against each sign-in field. Note that the logic is evaluated as Javascript, and can be used to compare numbers, strings, or Dates.
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In the case above, we've elected to check the "Temperature" sign-in field for answers greater than 100.4, and the "Certificate expiration" sign-in field for answers less than than the datetime of sign-in (Date.now() will be evaluated when the entry takes place). We're also checking the "Private Notes" section of the entry/invite—which is internal and not shown to the visitor—for the string 'deny.'
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For each of the logic checks you set up in step 3, select the action(s) you would like to take when the logic is met (deny entry and/or notify):
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In the example above, we've set it so that any answer to "Temperature" where the logic we set in step 2—in this case, where it's greater than 100.4—will deny the entry and notify someone (to be set in the next step). If the "Certificate expiration" answer logic is met—again, in this example, if the expiration occurred before the datetime of sign in—we will just notify someone. For a match on "Private Notes," we will just deny entry.
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Finally, for any "notify" actions you set in step 3, choose whom we should notify. We will attempt to notify that employee via the methods they've set up in their preferences.
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In this example, employee "Sam Kalum" will be notified for either rule.

Once you're done with step 4, don't forget to click "Complete Setup."