Abstract: A sensor provides a persistent indication that it has been exposed to temperatures exceeding a critical temperature for a predetermined time period. An element of the sensor made from shape memory alloy changes shape when exposed, even temporarily, to temperatures above the Austenitic temperature of the shape memory alloy. The shape change of the SMA element causes the sensor to change between two readily distinguishable states. The sensor includes a removable element that prevents the shape change, allowing the sensor to be manufactured and stored at temperatures above the Austenitic temperature without causing the indication of an over-temperature event.

Abstract: Shape memory alloy actuators comprising at least one hollow helical spring with an array of parallel shape memory alloy wires enclosed within or parallel and attached to each of the at least one hollow helical springs. Insulative end caps are attached to end of the at least one hollow helical springs, the insulative end caps defining electrodes for conducting electricity to the arrays of parallel shape memory alloy wires. Voltage means are connected to the electrodes for selectively providing electrical energy to the parallel array of shape memory alloy wires, causing the parallel array of shape memory alloy wires to expand and contract, providing either motion or measurement functions.