Abstract: One aspect of the invention involves: monitoring a voltage of a battery over time; evaluating whether a rate of voltage decrease of the battery is in excess of a threshold; and indicating that the battery is subject to a low voltage condition when the rate of voltage decrease exceeds the threshold. Another aspect of the invention involves: causing a circuit powered by a battery to respond to battery replacement by thereafter applying a selected load to the battery during a selected time interval. A further aspect involves: periodically sampling a voltage of a battery; and applying a load to the battery during a selected time interval before each sampling of the battery voltage.

Abstract: One aspect of the invention involves: maintaining a record of how long a circuit operates in each of a plurality of different operating modes thereof, starting from a point in time at which a battery that powers the circuit is replaced; calculating for each of the operating modes as a function of the record a cumulative current drain from the point in time to a current time; and determining as a function of the cumulative current drains whether the battery is subject to a low voltage condition. Another aspect involves: monitoring a voltage of a battery; periodically determining whether the voltage of the battery is subject to a low voltage condition; and maintaining a count of the number of times that the determining results in a determination that the battery is subject to a low voltage condition.

Abstract: A tag stores information identifying the sequence in which it received wireless signpost signals from different signposts. In another configuration, a tag maintains data identifying a group of signposts that are to be treated as equivalent. In yet another configuration, wireless signpost signals transmitted by each of a plurality of signposts all contain the same signpost code. In still another configuration, a signpost has an interface through which a signpost code of the signpost can be selectively set.

Abstract: A tag can transmit a tag signal, and responds to receipt of a wireless signpost signal by determining whether the signpost that generated the signal is currently active. When the signpost is respectively determined to be active and inactive, the tag respectively includes and excludes from the tag signal an information portion that relates to the signpost that generated the received signpost signal. In another configuration, a tag has first and second antennas, receives wireless signpost signals through at least one of the antennas, and responds to receipt of a signpost signal containing antenna select information by causing a selected one of the first and second antennas to be disabled and the other of the first and second antennas to receive wireless signpost signals.

Abstract: A tag receives a wireless signpost signal that contains a signpost code, converts the signpost code into location information representative of a physical location of a signpost that transmitted the received signpost signal, and transmits a wireless tag signal that includes the location information. In a different configuration, a tag receives a wireless signpost signal that includes a signpost code, and determines whether the signpost that generated the received signpost signal is a replacement for a different signpost. If it is a replacement, the tag transmits a wireless tag signal containing an information portion that relates to the signpost replaced by the signpost that generated the received signpost signal.

Abstract: One aspect of the invention involves: periodically sampling a voltage of a battery and an ambient temperature in order to obtain a sample that includes a temperature value and a voltage value; saving each sample in a sample group; selecting a subset of the samples in the group, wherein the temperature value of each sample in the subset is lower than the temperature value of substantially all of the samples of the group other than the subset; and determining as a function of the voltage of at least one the sample in the subset whether the battery is subject to a low voltage condition.