Based on FiltreteSmart, one would expect that the Filtrete “smart” filters that pair with FiltreteSmart would actually monitor the effective airflow through the filter and therefore give you a good idea of when they should be replaced. Alas, its just a gimmick that appears to simply start a countdown timer that expires after 90 days or so.
FiltreteSmart also supports an environmental air monitor, but the monitor itself (Speck) is no longer available. As such, this feature has no real use. Filtrete is apparently building their own monitor, which may or may not work with FiltreteSmart if/when they actually release it. But beware - the monitor is under development and being funded via an Indiegogo campaign, which is quite strange for a company as large as 3M to require this type of funding. I personally contributed to the campaign, had an issue and contacted Filtrete. They failed to stand behind their commitment, so I cancelled my contribution and will not buy the monitor if/when it is released. I recommend that others do the same - delete FiltreteSmart, purchase standard filters and just set a reminder on your calendar to replace your filters.