# [PHP], 61 bytes

<!-- language-all: lang-php -->

 for($a=$argn;($r=$i<strlen($a))&$a[$i++]==$a[$i++];);echo!$r;

[Try it online!][TIO-jz00zu0y]

[PHP]: https://php.net/
[TIO-jz00zu0y]: https://tio.run/##NchBCoMwEEDRqyQwFIP0BDF01xO4Ky7GOm2CITNk9PqNgnTz@HyJ0oaHnH64doABsH6L76AGSINuNVM5t3M3wBekvp9C@Jd3nt6RLVTf2jjGmJKqMZfLwrzv85wzkTGqIkSI62rtj2VLXLTdnwc "PHP – Try It Online"

Input string via `STDIN`, output is `truthy` (`1`) if it is double speak, and `falsey` (`0`) if it is not double speak. I'm just going to take the +1 byte and make it return an intuitive `1` or `0`... even I got confused testing it.

+1 byte fix for single character input.