Let's say I’m using a Dell Inspiron Laptop. Does my ISP have a log of this or can they detect what devices are connected to my router?
If you are using a modem and router provided by your ISP, then they can potentially have full access to data about your connected devices. This is because if you are using their device, then you don't really have a network of your own - your house is just an extension of their network. Some ISPs may use off-the-shelf hardware, in which case they may not take advantage of their access to your home. However, since they provided the hardware, they also have an opportunity to customize the firmware (the software running on the router) to do whatever they want. The router certainly knows about all the devices connected to it, and it would be very easy for them to customize the device to send them data about what devices are connected and when. It wouldn't surprise me if many companies do this for general data collection purposes or to look for violations of their terms of service. In many jurisdictions (especially the US), I'm sure doing so would be completely legal. Whether or not any particular ISP is actually doing this is another question, and difficult for us to answer.
Regardless of whether or not An ISP tracks your devices through your router, they can still see all of your network traffic of course. This means they can read any traffic that goes across in plain text (which primarily, but not exclusively, means HTTP). If you use their DNS servers (which will be the case unless you change it yourself) then they can also tell what sites you visit, even if over HTTPS. Lots of information about your devices can be gathered from your traffic, so they probably wouldn't have any trouble tracking connected devices exclusively through your HTTP traffic, as long as the devices are actively fetching data from the internet.
If you are concerned about the possibility, then the simplest solution is to use your own modem or router. Some ISPs effectively require use of their modem (for instance, I'm still using the modem provided by my ISP because it is difficult to find modems compatible with their network). Fortunately, using a different router is the important part. If you plug your own router into their modem and connect your devices only to your router, then you will make it much harder for your ISP to keep track of which devices are connected. After all, the only device they will directly "see" is your router.
Once you are using your own modem you can configure it to use a public DNS service (opendns or cloudflare for example). There is a lot of information hiding in your DNS queries, so this is an important step for the privacy-conscious.
If you really want to hide info from them though you'll mainly want to setup a VPN service 24/7. They must be properly configured to make sure you don't leak data though, so it helps to know what you're doing when setting one up. Personally I don't think that step would be worth it for the average user, but that's a decision for each person to make on their own, especially given recent news coverage about regulatory changes (at least in the US) that may give ISPs more rights to sell the data they collect about you.
Yes they do,
Actually in some places they are even required by law to identify and maintain a continuous record of all your hardware MACs and access times for criminal prosecution.
Actually there are multiple protocols designed for this purpose, like TR-069. https://en.wikipedia.org/wiki/TR-069
Yes your ISP can detect partially what devices you have plugged on your network. Here is a small list of basic techniques that they can use are:
- Check the User-Agent field of your HTTP traffic, the easiest.
- Check some of the TCP/IP fields in order to detect the operating system.
The effectiveness of them depends on the device and how secure have the communications with the outside world.
If you are truely paranoid, then yes, your ISP can detect and log any device connected to their router. They have full control over the router software, so they can install a spyware to upload them everything that the router could detect. At the simplest level, MAC address, and with little effort, the OS of the device, at a higher level, every shared disk or printer, and the router could even provide access to any shared disk.
Can reasonably such a spyware be installed by the ISP? Only my opinion, but I would think the risk very low and acceptable - but I have no atomic code on my devices...
It is as usual a matter of threat and acceptable risk level. If the most confidential data that is present on your devices are the messages you exchange with your lover(s), and the codes for your banking service, I would trust the ISP (after all, you chosed them, and confidential data should have an additional protection level). If you are hosting some top secret mission critical data, things are really different, and you should not trust the ISP provided router, and instead install a fully controled firewall between it and your internal private network.