Metal ions were important in a variety of chemical, biological, industrial, and environmental processes. Calcium and magnesium were the most important metal ions due to their importance in biological, environmental and chemical analysis. Many DNA-based sensors were used to detect metal ions over the last two decades. Apart from storing genetic information, the chemical structure of DNA had been shown to be ideal for metal binding via both the phosphate backbone and nucleobases. DNA was highly stable, inexpensive, and simple to modify. For metal sensing, two types of functional DNA were used: aptamers and DNAzymes. Because metal binding aptamers were difficult to isolate, only a few had been reported. While DNAzymes were effective metal sensing tools due to their catalytic activity, there was no need for metal immobilization. Each metal ion and the known DNA sequences for its sensing were discussed in this review. We concentrated on reviewing the majority of published calcium and magnesium detection sensors. Finally, several specific applications were discussed.