1. A tool for monitoring the presence of items, comprising: at least one receiver configured to receive information transmitted from at least two transmitters; one or more processors coupled to non-transient memory and the at least one receiver; a rule-based item co-location application comprising program instructions, stored in non-transient memory, that, when executed by the one or more processors, causes the one or more processors to: store in non-transient memory at least one rule relating to co-location of at least one item and the tool upon arrival at a future destination; receive location-based information transmitted from a first transmitter located in proximity to the future destination and determine that arrival at the future destination has occurred when the location-based information is received; in response to the determination that arrival has occurred, execute the at least one item co-location rule; receive item-based information transmitted from a second transmitter associated with the at least one item; in response to the determination that arrival has occurred, monitor for location-based information transmitted from the first transmitter and item-based information transmitted from the second transmitter; identify, based on the monitored location-based information, that the tool is no longer at the future destination when the tool is no longer receiving location-based information from the first transmitter; in response to identifying when the tool is no longer at the future destination, determine, based on the monitored item-based information transmitted from the second transmitter, whether the at least one item is co-located with the tool, wherein the at least one item is determined not to be co-located with the tool when the tool is no longer receiving item-based information from the second transmitter; and in response to the determination whether the at least one item is co-located with the tool, cause at least one alert to be generated if the at least one item is not co-located with the tool.