One of the major flaws of Pokémon GO is the fact that, at least until the arrival of Pokémon GO Plus, to find a Pokémon that appears in the game you need to always keep an open application on your smartphone, with the usual disastrous effects for the battery life.
Many have tried to solve this problem, especially for a way to save battery during sessions of Pokémon GO, but if you're one of those compulsive users huntering any kind of Pokémon, the PokeDetector application can be the ultimate solution for you. PokeDetector is indeed a free application that "replaces" accessory Pokémon GO Plus, even the option that lets you play with smartphone asleep when walking near a Pokémon, so that a notification will be sent to you to warn you that it has detected a Pokémon without opening it.
The application is made even more useful if you have an Android Wear smartwatch, as the alerts will come directly to your wrist, extending the options, and you can choose which Pokémon will get your attention without even having the phone in your pocket. Of course, developers are warned: the application is based on the use of unofficial Pokémon GO API, tool that could stop working if Niantic decides so, even causing problems with your account. Plus extras of Pokémon are shared among all players, you should login or register a new account "just in case", which is not actually used to play.
PokeDetector is available for free on the Play Store, but you can buy the Premium version at the price of 2.89 € to filter notifications based on Pokémon.