Why collect the MAC address of the mobile phone instead of collecting some more useful information, such as number, application, location? Not because the MAC address is more useful than this information, but because the more useful information cannot be collected on a large scale and in real time. To give a simple example, I have developed an APP for a mobile phone, which can naturally collect all relevant information. Why do I need to pay attention to the MAC address of this mobile phone at this time. However, you can't guarantee that most people have installed the APP, nor can you guarantee that the APP will be running all the time, giving you relevant information when you need it. For another example, if we provide a service, if the mobile phone is accessed, then we can know more information about the mobile phone (more useful than the mac address), such as the phone model, browser, mac, ip address such as. Also we cannot guarantee that most people will use this service. Relatively speaking, collecting the MAC address of the mobile phone is because collecting the MAC address can be done: simple, rough, real-time, and direct. This is stipulated by the 802.11 protocol, and all data packet transmissions are concentrated in 2. On the 13 channels on the 4Ghz frequency band, each data packet header has a mac address. As long as these data packet headers are obtained, and the data packet headers are not encrypted, the mac addresses of these mobile phones can be obtained. This has a great advantage: we do not need to make any assumptions or premise on the mobile phone in advance, there is no requirement to install the relevant APP or access the relevant service, as long as the wifi interface is turned on, we will The mac address of the phone can be collected non-stop. Of course, there is a premise that the mobile phone needs to send data packets, but this is not a problem, because even if it is an empty data packet, the mac address of the mobile phone can be obtained. For example, I collect the MAC addresses of all the mobile phones of people who enter the mall in the mall. Now, when people go shopping in the mall, they should bring their mobile phones. They only need to turn on the wifi, and no other requirements are required, so I can collect them in the mall. The activities of the people inside, if I solve the positioning problem again, I can even know how many people there are on this platform in the shopping mall at a certain moment, and what the circulation is, so as to calculate the specificity of my platform. Business situation (all positioning is difficult since we didn't do anything on the phone). And these are things that those service providers and apps can't do. One of the reasons is that the mac address is too easy to collect, and other information is collected with a lot of constraints. It is impossible for everyone to have it and provide it all the time, but the mac address can be used, which is the 802.11 protocol. of the. How to achieve it: 1. The public AP is directly used as a "device for mobile device MAC address", and can record the MAC address of each mobile phone associated with it, paving the way for subsequent analysis. Pros: There are no privacy issues, as most people actively connect. Disadvantages: high cost, limited range of one AP, and a lot of numbers required; moreover, it needs to provide Internet access function for each AP, which is too expensive. Because the mobile phone is connected only with the user's approval, it is basically impossible to obtain most of the mac addresses in this area, and there is a problem of data sparseness, which is not worth the loss. 2. Impersonate some commonly used APs and do not provide Internet access functions, such as your wifi in Starbucks, mobile APs, I can provide APs with the same SSID in other places, the mobile phone will automatically associate with the previous records, just pay attention to the ssid duplicate situation. Advantages: Because there is no need to provide Internet access, the cost is very low; Disadvantages: This situation is definitely illegal (although I don't know the relevant laws). 3. wifi sniffer. To put it simply, the current data packet header is not encrypted. After we use sniffer to detect the data packet, we directly get the relevant information of the hand sending the data packet from the packet header, including: mac address, destination address AP's ssid, signal strength class information. The means of monitoring is very simple. All wifi data packet transmissions are concentrated in 13 channels (mainly 1, 6, 13). Any device with wifi can monitor these data packets, such as mobile phones, Laptops, portable wireless network cards, etc. Advantages: low cost; very convenient, it is possible to do large-scale listening, because there is no need to do association operations. Cons: There are also privacy concerns. What kind of technical problems exist: (No matter which method is used, there are all of them. Here I will mainly talk about the technical problems of the third method.) First, the positioning is difficult. Even if sniffer monitors the data packets of your mobile phone, it is difficult to accurately locate the location of your mobile phone. The reason is very simple. A data packet only has the ssid and signal strength of the AP, so it is inaccurate to speculate the location of your mobile phone. Whether it is indoor positioning or outdoor positioning, the pre-set wifi profile and the current mobile phone to multiple APs and their corresponding signal strengths are required, otherwise the positioning will be inaccurate and it will not make much sense. General wifi positioning: the mobile phone needs to send a probe request to the AP, find the APs and the corresponding signal strength of the current network around the mobile phone, and then push out the current location information according to the offline or online wifi profile; the cooperation of the client, namely the mobile phone, is required here. Without the cooperation of mobile phones, it is a difficult problem to rely on external equipment to push out the location of mobile phones. Secondly, your phone will not be sending data packets all the time. If I use a simple long-tailed distribution to assume the time to send a packet for a phone, then even if there is wifi in one place Sniffer's devices also detect mobile phone user activity is also sparse. Of course, if a user comes and goes frequently, the data obtained by the mobile phone user is still very valuable. But on the street, it doesn't make sense, but it's valuable in the mall. Finally, the data is huge. Really big. Since most of the phones we listen to are within range, this magnitude is huge. To make a simple comparison, in a shopping mall, one is to monitor the mac of all mobile phones, and the other is to use the APP to monitor the information of mobile phones. Calculate the number of people in the mall, and compare the data of the APP installed with the total number. This app also runs and compares the total, which is not an order-of-magnitude comparison. With the expansion of the monitoring range, the amount of data is naturally very large. Secondly, a lot of redundant data, because we only need the mac address of the mobile phone, and the change of the signal strength over time, and do not need the content of the data packet (of course you can't know it because it is encrypted), which often results in a lot of data packets, There is no value, while valuable packets are often not sent. It is still difficult to analyze. Regarding its privacy and commercial future: this one has been said a lot by others, let me talk about my own views. Privacy: There must be a problem. Basically, the mac address can be used to calculate the approximate activity range of the mobile phone holder (which cannot be accurately done), the range of home, the range of work, and so on. I don't know how to deal with it legally or morally. If you don't want your mobile phone's mac to be monitored, there is no other way than turning off the wifi interface. Business: Business behavior is generally to build some services (or APP) and provide them to the mobile phone, then access to the mobile phone of this service, we can get most of the useful information of the mobile phone. In one section, many of the answers to this question are explained from this perspective. But what I want to say is that if you are only providing services, you don't need to care about the mac address of the phone, because the value of the mac address is lower than other information. My suggestion: use the method of association, build services by yourself, and have a batch of user data (increase access to your own services), but in a batch of users, relative to the overall number of people, only a small number of people. Whether it is a public AP, or pretending to be an AP or wifi sniffer, it can be associated with existing users, and promote corresponding business activities in the area monitored by itself.