For stay at home working moms, how do you keep your toddlers busy while you work and no one is available to look after them?

I generally used to have my kid at a place where I could see him all the time. And if that wasn't possible I used to check him every now and then wile I was cooking in the kitchen or doing some other errand. And when she was less than a year, I would let her sit in the baby cot and used to take it in whichever room I was working. Later, I had a stroller where I used to keep the toys she needed and stuff and take him wherever I used to be. And when this wasn't required, I used to make him sit on a mattress on floor (to avoid any chance of falling) and place his toys, or handing him something to eat. It kept him busy for quite some time. Give baby blocks or talking toys.