Thirty days, up to three emails a day delivered as phone calls, free dial-in, and no credit card to start.
A trial account can add a second phone number and create filters, so the two things most people want to test before paying, escalation to a colleague and routing by subject line, can both be tried on the trial. Three calls a day is enough to prove a monitoring tool or a sensor gateway reaches the phone; it is not meant for live alerting, which is what a plan is for.
Nothing is charged when the trial ends, because no card was taken. Choose a plan from $10 a month to continue; billing explains how the month is charged. Start the trial on the signup page.