Temperature measurement is the best way of ensuring food, particularly lumps of meat, are 'cooked' and I use one of the fast Thermopen models here thermapen.co.uk/thermapen-thermometers/1-thermapen-thermometers.html there are similar much cheaper models available but they take 10-15 seconds to read the proper temperature. However, measuring the internal temp of a steak is not as easy as it sounds due to the thickness (or should that be thinness?) of most steaks.
I prefer my steaks grilled rather than pan seared. I love the char you can get from grilling vs. the crust you get from searing. Here's my method:
Get steaks to room temp, rub in olive oil, rub fresh garlic on them, kosher salt and freshly cracked black pepper. Let steaks sit for 15-30 minutes. While waiting, pre-heat grill on high for at least 10 minutes with lid closed, get it nice and hot. Throw on the steaks, grill on high direct heat, lid closed, about 3 to 4 minutes per side depending on thickness and how hot your grill can get. And, as always, let steaks rest for 5-10 minutes before eating. Lats step is very important.