If you are convicted of aggravated DWI or second/subsequent DWI in New Hampshire, you will be ordered to install an interlock device in your car before you can drive again. This costs around $100 a month and you will need it for 1-2 years. You need it on any car you drive. The machines are presently not smart enough to know who is driving, so anyone who uses the car/vehicle will have to blow into it. If the machine determines you drove with alcohol in your system, it will flag it and the car will not start/ will shut down. You can be called in to the DMV for a hearing regarding a positive result. Even though the machine has false positives, especially things like cologne, you can still lose your license for testing above the low limit. (Also, you will have been on probationary license and your legal limit is well below .08).
Even if you are found guilty of a first offense DWI, the judge has discretion to order you to install the interlock before you get your license back. If you manage to not have the judge order an interlock, under the new laws the DMV can still call you in for an interlock hearing. They are particularly likely to do this if you have a previous alcohol related offense, if your aggravated dwi was reduced to a standard dwi, or if you had a second offense reduced to a standard dwi. If you get invited to one of those DMV hearings, you have the right to hire a lawyer to represent you. I have been told that the DMV has been ordering interlocks in around 50% of the hearings where people show up and can demonstrate the public would not be safer with one. (If you ignore the hearing, you are probably close to a 100% likely to get the interlock ordered and required before you can get your license back. )
Pretty much the only sure way to not get an interlock device is to not be found guilty of driving while intoxicated.