A method for initiating a thermal battery including: releasing an engagement between an element and a striker mass upon an acceleration time and magnitude greater than a first threshold; and moving at least one member into a path of the element to prevent the element from releasing the striker mass only where the acceleration time and magnitude is greater than a second threshold, the second threshold being greater than the first threshold.

Methods, systems, and devices are disclosed herein for incorporating a power-saving sleep mode into electronic devices using an activity-based switch device. These switch devices may have with a communication module having more advanced electronics, such as wireless communications features. These switch devices may be built into electronic devices and/or batteries during manufacture, and/or may also be retrofitted into already existing electronic devices and/or batteries. A switch device may be placed between a power source, such as a battery, and the electronic device. When activity or motion is detected, the switch closes to connect the power source to the electronic device, thus turning the portable electronic device “on” as normal. However, when activity is not detected for a meaningful amount of time, the switch opens and disconnects power from the electronic device to conserve power, thus placing the portable electronic device into a power-saving sleep mode to conserve the power source.

The technology relates to techniques for an electromagnetic inertial switch. An electromagnetic inertial switch can include an electrically conductive and magnetic mass located within a cavity, where portions of the cavity are electrically conductive and are electrically coupled to terminals of the electromagnetic inertial switch. A first magnetic field can be configured to apply a first force on the mass to attract the mass towards a first location, and a second magnetic field can be configured to apply a second force on the mass to attract the mass towards a second location. The electromagnetic inertial switch can be in a first electrical state when the mass is in the first location, and in response to an acceleration event greater than a threshold acceleration, the mass can move to the second location, thereby changing the electromagnetic inertial switch to a second electrical state.