Google Shopping now has a new feature that allows consumers to check a box to get notified if a price has dropped.
As of writing only mobile devices are supported. Desktop searches do not have this available.
Just underneath the visit site or add to cart button, it will have a Track Price toggle. As shown in the animation below.
As of writing, merchants will not be able to know how many have toggled on the track price feature. So to benefit from potential extra sales is to sporadically reduce your price by x amount of percentage. If you want to enjoy both the track price feature and an automated promotion feature. Then reduce the price by at least 10%.
And let this run for a few weeks. Then increase the price again to the original price.
As this is a new feature you may or may not get results. As the adoption may be a bit slow. My recommendation is to test this with your most sold and profitable products every month or few months and see the effects.
When you do experiments, make sure you collect data that is long enough. For example, if you only create a price drop for a few days, you may not really see what is going on. Experiments are best done with a duration of 2 to 3 weeks.