This app was mentioned in 6 comments, with an average of 1.50 upvotes
I have the PS Deals app on my phone and it allows you to add your wishlisted games to the app and it will notify you as soon as any of the games get a price drop.
Here is a link to the Andrioid version of the app.
I really like the app because it usually notifies me of price drops before before the story has finished updating, before the discounts are even viewable on the PSN website or on the PS Store on consoles.
I imported my GOG and Steam wishlists into isthereanydeal.com and receive an email whenever my wishlisted games go on sale. Not quite as good as notifications on my phone, but as long as you check your email daily, you shouldn't miss any price drop alerts.
Is this apple only?
Edit: Looks to be that way. There's this for Android users, but it only works for Playstation store deals.
Download the app called PS Deals. You can add your wishlisted games to the app and it will send you a notification within seconds of a game dropping in price.
I've had this app on my iPhone for years and it usually sends me notifications before the PS Store has even updated to the point that I can see the prices myself.
PlayStation Deals Android ...not tracker app ... shows when sales are on
I recommend you "Play Deals" for Android
https://play.google.com/store/apps/details?id=br.com.lucascardinali.alpha