In criminal cases where a recognizance for the appearance of any person, either as a witness or to appear and answer, shall have been taken and a default entered, the recognizance shall be declared forfeited by the court, and at the time of adjudging such forfeiture said court shall enter judgment against the principal and sureties named in such recognizance for the sum therein mentioned, and execution may issue thereon the same as upon other judgments. If the surety is not notified by the court in writing of the unexplained failure of the defendant to appear within thirty days of the date for appearance, then the forfeiture shall be null and void and the recognizance exonerated.