There is a single probe on the forward left hand side of the fuselage which senses ice formation
There is in fact 2 ice detectors, one on either side of the fuselage.
The aircraft has Nacelle Anti-Ice which is not automatic like the 777. Nacelle Anti-ice is hot bleed air. It is used when the temp is below 10 oC.
NAI is automatic, the control switches on the overhead panel are three position off/auto/on. in auto NAI is controlled by the ice detectors.