Better have something that runs off the cloud. PagerDuty is not something under your countrol. A stuff as imporant as dead man switch should not rely on someone's service.
Okay, so now your dead man’s switch depends on your home or colo’s power, internet connection, compute hardware, storage hardware, network hardware, software stack maintenance, plus the ability to pay bills for those on time?
Pre-Paying a cloud service pennies per month to do all that for you will likely be more reliable and much simpler.
I'd argue entirely opposite, that a dead man's switch should 100% rely only on someone else's services and should avoid any dependencies on your stuff, as something happening to you is correlated to something happening to things you run or own, and the whole point of such a switch is that it should function properly when e.g. all your stuff burns down or gets confiscated or whatever.