Which is not a valid method for detecting smoke or flame?

A.
Temperature

B.
Ionization

C.
Photoelectric

D.
Ultraviolet

Explanation:
Answer A is correct; temperature sensors are used in heat detectors, not in smoke or flame detectors.

Incorrect Answers and Explanations: B, C, and D: Answers B, C, and D are incorrect. Ionization and photoelectric sensors are used in smoke detectors. Ultraviolet sensors are used in flame detectors.