Easy, something like twilio to grab all SMS messages, and react on either any message being sent, or a specific message being sent. I guarantee you someone in jail can find a way for someone to send a text.
Looks like you didn't read OP carefully.
I know there are already a nice set of solutions, which include at least:
[...]
- Pre-signed transaction "bombs" that an accomplice can trigger on a "jailed man switch".
Any idea that does not implicate a "trusted 3rd party", now ?
Just you, your fat wallet, and some people determined to gain access to said wallet.