Is it possible to call 110 without a SIM card?
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"Mobile phones have always had an emergency call function, but why can't we dial emergency numbers such as 110, 120, 119, etc. when there is no mobile phone signal or the SIM card is removed? In fact, a mobile phone can still make a limited number of emergency calls without a card, and the numbers dialed vary depending on the mobile phone. However, it is indeed impossible to make emergency calls when there is no network signal. We will save this question for the end to answer, and first briefly explain to you how the emergency call works. How does a mobile phone make an emergency call? As long as the mobile phone is turned on normally, the first thing to do is to detect whether there is a SIM card, search for the network, and register the process. According to the priority of the SIM card, select the appropriate network for registration and authentication until the registration succeeds or fails, in this order. The SIM card is just an authentication link here. Whether there is a SIM card or not, it will not affect the normal operation of the mobile phone's RF module. When the mobile phone's RF module is working normally, it can search for the surrounding network signals, and can initiate a call state with the established network at any time, so that the mobile phone can initiate a call with the network. However, if you want to make a call through the Internet, you must meet the specific conditions of the network operator. The role of the SIM card is only to tell you who the base station is, and it does not assume the role of the communication module. To give a simple example, the signal is like navigation, which will search for the place you want to go, and the SIM card is the door card of this place. Without a SIM card, you just can't enter, but it doesn't prevent you from finding the address. Since emergency calls have a very high priority, operators have very few restrictions on emergency calls, and do not need to register. Without registration, there is no need for a SIM card to complete the mutual authentication between the mobile phone and the network side, so you can dial emergency numbers without a SIM card. By dialing the emergency number, the network established by the mobile phone will automatically identify the emergency number and use the base station to roughly locate the location of the calling user, and then connect this number to the nearest service station, so that an emergency call can be made. When there is no card, the signal is not displayed, which is not really "no signal". When it shows "Dial emergency numbers only", it means that the mobile phone can still search for surrounding network signals. The real lack of signal is when the phone displays "No Network", and in the case of a real lack of signal, you cannot dial the emergency number. So why sometimes you cannot dial 110 after removing the SIM card? In fact, the emergency numbers we imagine are generally 110, 120, and 119. The correct term for this type of number is "special service number", not an emergency number, so such phone numbers can only be successfully dialed by China Telecom's 3G and 4G mobile phones, and other phones cannot be dialed without a card. The reason why other mobile phones cannot dial is that China Unicom and China Mobile are in compliance with the 3GPP protocol in terms of network standards. The 3GPP protocol only stipulates that the emergency numbers are 911 and 112, so dialing 110, 119, and 120 cannot be connected. As for why there is an artificial voice when dialing the 112 emergency number without a card, the reason is that the domestic emergency number line is set as an automatic voice station, which is of no use, but when you hear this voice, it means that your emergency number has been dialed. As for 110, which cannot be dialed, you can try dialing 112. It is strongly recommended that users of China Telecom mobile phones try to dial 110, because it will work. In addition, I will insert a digression about dialing 110 by mistake: I once dialed 10086 and it became 11086. After the call was connected, I thought it was a manual customer service of China Mobile. I foolishly told the other party that I wanted to check the phone bill. The other party told me that it was a call for the police... I was so scared that I almost peed my pantsΣ(° △ °|||)︴ As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity. |
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