EMI and RFI testers monitor the presence of unwanted electromagnetic interference (EMI) and radio frequency interference (RFI). EMI and RFI is electromagnetic radiation emitted by electrical circuits which, as a by-product of normal operation, carry quickly-changing signals that cause interference or noise in other circuits. EMI and RFI interrupts, obstructs, and limits the effective performance of these other circuits. EMI and RFI can be induced intentionally, as in electronic warfare, or unintentionally, as a result of spurious emissions and responses. EMI and RFI testers identify interference that could potentially cause a failure, which might interfere with medical equipment or halt a manufacturing process.