This paper presents an analysis of the impact of selective software-based techniques to detect faults in microprocessor systems. A set of algorithms is implemented, compiled to a microprocessor and selected variables of the code are hardened with software-based techniques. Seven different methods that choose which variables are hardened are introduced and compared. The system is implemented over a miniMIPS microprocessor and a fault injection campaign is performed in order to verify the feasibility and effectiveness of each selective fault tolerance approach. Results can lead designers to choose more wisely which variables of the code should be hardened considering detection rates and hardening overheads.