Praise be to Allah

Firstly: 

Counting the number of rak‘ahs in the prayer is something for which there is a precedent in the practice and words of the early generations. Their methods of counting varied according to their environments and times. Some of them used to use their rings, some used date stones or pebbles, and others used their fingers or toes. All of this confirms that there is a basis for using such a device to count the number of prostrations and rak‘ahs. 

Ibn Rajab al-Hanbali (may Allah have mercy on him) said:

Al-Fadl ibn Shaadhaan quoted in his book ‘Add al-Aayi wa’r-Rak ‘aat fi’s-Salaah the hadith of ‘Abd ar-Rahmaan ibn al-Qaasim from his father, from ‘Aa’ishah, according to which, when she offered an obligatory prayer, she would count her prayer with her ring, moving it on her hand until she finished her prayer, and counting with it.

End quote from al-Khawaatim by Ibn Rajab (p. 109). The isnaad going back to ‘Aa’ishah is saheeh. 

Al-Kharashi al-Maaliki (may Allah have mercy on him) said:

Moving the ring from one finger to another in order to count the rak‘ahs when one is afraid of forgetting does not come under the heading of fidgeting, because that is being done in the interests of the prayer.

End quote from Sharh Mukhtasar Khaleel (1/294) 

In Haashiyat Ibn ‘Aabideen (1/650) it says: 

It says in al-Bahr: With regard to moving the tips of the fingers (to keep count) or counting in one’s mind, that is not makrooh, according to consensus, but counting out loud spoils the prayer, according to consensus. End quote. 

Muhammad al-Baabirti al-Hanafi (may Allah have mercy on him) said:

… It was narrated from Abu Yoosuf and Muhammad that there is nothing wrong with counting on the hand. He mentioned the hand specifically, because moving the tips of the fingers (to keep count) or counting in one’s mind is not makrooh, according to consensus, but he warned against counting out loud, because it spoils the prayer.

End quote from al-‘Inaayah Sharh al-Hidaayah (1/418) 

Shaykh al-‘Uthaymeen (may Allah have mercy on him) said:

He may count the number of rak‘ahs, and there may be a need to do so, because many people may forget and resort to counting them on their fingers, in which case there is a problem, because when the worshipper bows, he has to spread his fingers, and when he prostrates, his fingers must be straight. Therefore he may count them using pebbles or date stones. So he can put four dates stones in his pocket, then when he has prayed the first rak‘ah, he can move one of them, and so on until they are finished. There is nothing wrong with this, because there is a need for it, especially when one is very forgetful. 

End quote from ash-Sharh al-Mumti‘ ‘ala Zaad al-Mustaqni‘ (3/249, 250). 

Secondly: 

But in the case of this counter and similar inventions, there are a number of concerns: 

1. The worshipper may be distracted by looking at it and thinking about its numbers. In most cases he will not be content with the number of the sajdah or rak‘ah until he thinks it over so that he may be sure that it is correct. This is something that may cause the device to miss its original purpose, which is to help one to focus in prayer and not be distracted by anything outside the prayer.

2. There are essential parts and obligatory acts in the prayer that the device does not take into account. There may be a mistake in the recitation of al-Faatihah, or the worshipper may forget to sit for the first tashahhud, or he may not bow at all, but the device may count it as a rak‘ah because he prostrated twice! In which case the benefit from it may be limited or completely absent. Similar problems may arise if there is a prostration of recitation (sujood at-tilaawah) during the prayer.

Thirdly: 

With regard to our opinion concerning this device and similar devices, we say: 

Islam came to enjoin presence of mind when praying, and it has prescribed clear rulings for the one who loses focus and makes mistakes in his prayer. If he loses focus and does not know how many rak‘ahs he has prayed, then he should proceed on the basis of the lower number, then do the prostration of forgetfulness before saying the salaam. It is also prescribed for him to seek refuge with Allah from the Shaytaan and to spit drily to his left when he realises that he has become distracted in his prayer. 

What we think is that it is permissible and useful for one who is faced with compulsive whispers, or is very forgetful and that is causing him some difficulties, if it will benefit him in his prayer and will fulfil its purpose by helping him to focus on his prayer. But in ordinary cases, when there is no particular need for such things, we do not think that a person should use it; rather there is the fear that it may come under the heading of blameworthy unnecessary effort and things that people have introduced into the matter of worship that are detrimental to the original purpose of focusing the heart on Allah, and praying with proper humility, so you see him giving free rein to the thoughts and whispers that come to him, relying on the device to count his prayer for him! 

And Allah knows best.