What does a tech do? Why at an ER?
it can vary depending on how major/well-funded the hospital is. if i were you i would try to be at a Level I Trauma Center (able to take anything and everything).
at any ER, as a tech you will be doing some menial work like putting clean sheets on beds and stocking shelves. at rich/small ERs, it's likely that this is ALL you'll be doing (in addition to observing, of course). i worked at a private hospital system that i get the impression was not rolling in dough - the ER wasn't chronically understaffed by any means, but when things got really busy all hands had to be on deck providing medical care.
i learned all manners of venipuncture and got quite good at it, in addition to running blood and urine samples (for urinalysis, blood sugar, cardiac markers, etc) doing EKGs, orthostatics, assisting ortho PAs, cleaning and bandaging, cutting clothes off trauma patients, doing chest compressions, even taking blood pressure by auscultation when it was too low for the machines to get. not saying this is typical - but possible if you show some interest and pluck. the more hectic and underfunded the ER, the more likely you'll get some great hands-on experience.
if the docs are cool you can also get some early experience reading x-ray and CT results (impossible at first. what?! that spot is a bleed?), as well as observing the management of every chronic and acute condition imaginable. you'll also see them deal with drug seekers and other people abusing the system (one of my favorite examples is a couple - adults - who came in and got VERY impatient with us because we took too long to serve them. chief complaint? they both had toothaches.) you also get to see all the way up the ladder from 3rd and 4th year med students to interns to residents to attendings. and the nurses (regardless of your sex) will flirt with you endlessly. the ER's just a great place to be.