Is there a module or some other support for putting a "debug break" statement in a script?

I'm playing around with an emulator and I'd like to be able to put break statements into the code being emulated to aid debugging the emulator. I can simply set a debugger breakpoint on a suitable statement in the emulator where the emulated break statement is parsed. But that needs me to set the breakpoint every time I start a debugging session. I'd rather have the breakpoint baked into the emulator code in some fashion.

Update: Corion in the CB pointed me at $DB::single = 1; documented in perldebug. This does exactly what I want including having no effect when I'm not running under the debugger.