Yes, a converter would work, but you can also use relays if you have any of those on hand. With 4-wire detectors you’d have a relay connected to the smoke detector power output terminals on your panel, which would be controlling the detector’s power from an external power source such as a 9V/12V battery or a 12VDC power supply. The alarm output terminals would be connected to the zone in the normal way. I think there’s a way of doing this with 2-wire detectors as well but I think it’d be much more complicated, too complicated for me to lay out here.
In addition, both methods can be used with alarms too; in terms of using a relay, you’d do the same as above but with a notification appliance in place of the smoke detector. I’ve often done this whenever I’ve wanted to use a non-24VDC alarm with my 24VDC panel, such as a 12VAC Edwards Adaptahorn I have.