The present invention provides a detection system for a PCR process using FRET which comprises at least two single-labelled Oligonucleotide sequences of differing Tm that hybridize to one another in free solution to form a fluorescent quenched pair, that upon introduction of a complementary sequence to one or both sequences generates a measurable signal, one of the sequences being of a Tm that is below the Ta of the PCR process, the other not being below the Ta of the PCR process.